Optical disk apparatus

ABSTRACT

An optical disk apparatus comprising a device for moving a focal point of a light beam for reproducing information recorded on an information face of a disk, in the direction perpendicular to the information face; a device for detecting a reflected light from the disk; and a device for discriminating whether the disk set in the apparatus is a disk having a thick base substrate or a disk having a thin base substrate. In this apparatus, a maximum value AS1L max  of an output signal from the reflected light detecting device and a maximum value ENV max  of an amplitude of an information reproducing signal are detected while driving the focal point moving device so that the focal point passes through the information face, and the discriminating device discriminates whether the disk set in the apparatus is a disk having a thick base substrate or a disk having a thin base substrate, on the basis of the ratio of ENV max  to AS1L max . Therefore, it is possible to discriminate between a DVD having a thin base substrate and a CD having a thick base substrate.

[0001] This is a Rule 1.53(b) Divisional of Ser. No. 08/687,028, filedJul. 25, 1996.

FIELD OF THE INVENTION

[0002] The present invention relates to an optical disk apparatus thatreproduces different kinds of disks, such as a compact disk and adigital video disk.

BACKGROUND OF THE INVENTION

[0003] There is an optical disk apparatus in which a light beam emittedfrom a laser is focused on a rotating disk to reproduce signals recordedin the disk.

[0004]FIG. 25 is an enlarged view of a part of a typical compact disk(hereinafter referred to as CD). In the figure, reference numeral 1designates a base substrate of the CD, numeral 2 designates aninformation surface, and numeral 3 designates a series of pits on theinformation surface. These pits 3 provide a spiral track. The pitch ofthe spiral track is 1.6 μm. Aluminum is vapor-deposited on theinformation surface 2 as a reflecting film. The rear surface of thedisk, opposite the information surface 2, is irradiated with a lightbeam. When information recorded on the track is reproduced, focusing isperformed so that a focal point of the light beam is always positionedon the information surface 2 where the Al reflecting film is present,and tracking is performed so that the focal point of the light beam ispositioned on the track. The diameter of the disk is about 120 mm, andthe thickness of the base substrate 1 is 1.2 mm. The wavelength of thelight beam is 780 nm.

[0005] In recent years, disks with high recording density, for example,a digital video disk (hereinafter referred to as DVD) in which digitalimage data are recorded, have been proposed. Hereinafter, a DVD will bedescribed as an example of a high recording density disk. However, thepresent invention is not restricted to a DVD.

[0006] The recording density of the DVD is about five times as high asthat of the CD. In order to achieve this recording density, the trackpitch is reduced to 0.74 μm and the track recording density (number ofdata on the track per a unit length) is increased. With the increase inthe recording density, the wavelength of the light beam is reduced to650 nm. In order to reliably reproduce information recorded in the diskeven when the disk is inclined, the thickness of a base substrate of thedisk is 0.6 mm, that is, thinner than that of the CD. The diameter ofthe DVD is approximately equal to that of the CD. Hereinafter, this DVDis called a single-layer DVD.

[0007] Besides the single-layer DVD mentioned above, there is also adouble-layer DVD as shown in FIG. 26. In FIG. 26, reference numeral 4designates a first layer, numeral 5 designates a second layer, numeral 6designates an intermediate layer, and numeral 10 designates a basesubstrate of the DVD. The DVD is irradiated with a light beam at therear surface of the base substrate 10. Like the single-layer DVD, thefirst layer 4 wherein information is recorded is 0.6 mm distant from therear surface of the base substrate 10. A reflecting film comprising Auor the like is employed as the first layer 4, and the reflectivity isreduced to about 35%. So, a part of the light beam passes through thefirst layer 4. This first layer serves as a first information surface.The second layer 5 is located on the first layer 4 with the 40 μm thickintermediate layer 6 between them. The light beam passing through thefirst layer 4 is reflected by the second layer 5 and travels through theintermediate layer 6, the first layer 4, and the base substrate 10. Thissecond layer serves as a second information surface. Thereby,information recorded in the first layer 4 and the second layer 5 can bereproduced. The second layer 5 comprises aluminum or the like, and thereflectivity is about 90%. The recording capacity of this double-layerDVD is about twice as large as that of the single-layer DVD. In thisdouble-layer DVD, when information recorded in the first informationsurface 4 is reproduced, focusing is performed on the first informationsurface 4. When information recorded in the second information surface 5is reproduced, after the focal point is moved from the first informationsurface 4 to the second information surface 5, focusing is performed onthe second information surface 5.

[0008] When a CD and a DVD are reproduced using an optical diskapparatus, the apparatus is provided with an optical system forreproducing the CD and an optical system for reproducing the DVD becausethe CD and the DVD have different base material thicknesses, and theoptical systems are switched according to a disk set in the apparatus.In order to identify whether the disk set in the apparatus is a CD or aDVD, a cartridge containing the disk has a hole for discrimination.

[0009] However, when the disk is not contained in a cartridge, it isimpossible to identify the disk using a cartridge. If the optical systemfor the DVD is used for the CD, information is not correctly reproducedbecause of the difference in base material thicknesses between the CDand the DVD.

[0010] Meanwhile, there is a disk called CD-R which is a recordableoptical disk of write once read many type. When the CD-R, which employsthe same optical system for the CD, is set in the optical diskapparatus, if the optical system for the DVD is selected by mistake,information recorded in the CD-R is sometimes destroyed. Thisdestruction is attributed to the fact that the CD-R usually employs, fora recording film, an organic coloring material that highly absorbs lighthaving a wavelength of 650 nm and, therefore, the recording film iseasily destroyed.

SUMMARY OF THE INVENTION

[0011] An object of the present invention is to provide an optical diskapparatus that can discriminate between a CD and a DVD even when thesedisks are not contained in cartridges.

[0012] Another object of the present invention is to provide an opticaldisk apparatus that can discriminate between a CD-R and a DVD withoutdestroying an information surface of the CD-R when the CD-R is set inthe apparatus by mistake.

[0013] Other objects and advantages of the invention will becomeapparent from the detailed description that follows. The detaileddescription and specific embodiments described are provided only forillustration since various modifications within the scope of theinvention will be apparent to those of skill in the art from thedetailed description.

[0014] According to a first aspect of the present invention, there isprovided an optical disk apparatus comprising means for moving a focalpoint of a light beam for reproducing information recorded on aninformation face of a disk, in the direction perpendicular to theinformation face; means for detecting a reflected light from the disk;and means for discriminating whether the disk set in the apparatus is adisk having a thick base substrate or a disk having a thin basesubstrate. In this apparatus, a maximum value AS1L_(max) of an outputsignal from the reflected light detecting means and a maximum valueENV_(max) of an amplitude of an information reproducing signal aredetected while driving the focal point moving means so that the focalpoint passes through the information face, and the discriminating meansdiscriminates whether the disk set in the apparatus is a disk having athick base substrate or a disk having a thin base substrate on the basisof the ratio of ENV_(max) to AS1L_(max). Therefore, it is possible todiscriminate between a DVD having a thin base substrate and a CD havinga thick base substrate.

[0015] According to a second aspect of the present invention, there isprovided an optical disk apparatus comprising means for moving a focalpoint of a light beam for reproducing information recorded on aninformation face of a disk, in the direction perpendicular to theinformation face; means for detecting a reflected light from the disk; asignal detecting means for detecting a prescribed frequency componentfrom an output signal from the reflected light detecting means; andmeans for discriminating whether the disk set in the apparatus is a diskhaving a high track recording density or a disk having a low trackrecording density. In this apparatus, the discriminating meansdiscriminates whether the disk set in the apparatus is a disk having ahigh track recording density or a disk having a low track recordingdensity on the basis of an output signal from the signal detecting meanswhen the focal point moving means is driven so that the focal pointpasses through the information face. Therefore, it is possible todiscriminate between a disk having a high track recording density and adisk having a low track recording density.

[0016] According to a third aspect of the present invention, there isprovided an optical disk apparatus comprising means for moving a focalpoint of a light beam for reproducing information recorded on aninformation face of a disk, in the direction perpendicular to theinformation face; means for detecting a reflected light from the disk;means for digitizing an output signal from the reflected light detectingmeans; means for measuring a high level period or a low level period oftime for an output signal from the digitizing means; and means fordiscriminating whether the disk set in the apparatus is a disk having ahigh track recording density or a disk having a low track recordingdensity. In this apparatus, the discriminating means discriminateswhether the disk set in the apparatus is a disk having a high trackrecording density or a disk having a low track recording density on thebasis of a signal output from the period measuring means when the focalpoint moving means is driven so that the focal point passes through theinformation face. Therefore, it is possible to discriminate between adisk having a high track recording density and a disk having a low trackrecording density.

[0017] According to a fourth aspect of the present invention, there isprovided an optical disk apparatus comprising means for moving a focalpoint of a light beam for reproducing information recorded on aninformation face of a disk, in the direction perpendicular to theinformation face; means for detecting a reflected light from the disk;and means for discriminating the disk set in the apparatus as a diskemploying an organic coloring material for a recording film when asignal output from the reflected light detecting means when the focalpoint moving means is driven so that the focal point passes through theinformation face is lower than a prescribed level. Therefore, it ispossible to discriminate a CD-R in a relatively simple structure.

[0018] According to a fifth aspect of the present invention, theabove-mentioned apparatus further comprises a focus error signaldetector detecting a focus error signal that shows a focused state ofthe light beam irradiating the information face of the disk on the basisof the output signal from the reflected light detecting means, and thediscriminating means discriminates the disk set in the apparatus as adisk employing an organic coloring material for a recording film when anamplitude of the focus error signal is lower than a prescribed level.Therefore, it is possible to discriminate a CD-R in a relatively simplestructure.

[0019] According to a sixth aspect of the present invention, in theabove-mentioned apparatus, the discrimination of the disk employing anorganic coloring material is performed with a light beam having anintensity lower than the intensity of the light beam for reproducing theinformation. Therefore, even when the disk set in the apparatus is aCDR, information recorded in the CD-R is not destroyed when the disk isdiscriminated.

[0020] According to a seventh aspect of the present invention, there isprovided an optical disk apparatus comprising means for moving a focalpoint of a light beam for reproducing information recorded on aninformation face of a disk, in the direction perpendicular to theinformation face; means for detecting a reflected light from the disk;and means for discriminating whether the disk set in the apparatus is adisk having one information face or a disk having two information faces.In this apparatus, the discriminating means discriminates the disk setin the apparatus as a disk having two information faces when a signaloutput from the reflected light detecting means when the focal pointmoving means is driven so that the focal point passes through theinformation face is lower than a prescribed level. Therefore, thediscrimination between a single-layer DVD and a double-layer DVD can beperformed using the maximum value of the ENV signal, in a relativelysimple structure.

[0021] According to an eighth aspect of the present invention, theabove-mentioned apparatus further comprises a focus error signaldetector detecting a focus error signal that shows a focused state ofthe light beam irradiating the information face of the disk on the basisof an output signal from the reflected light detecting means, and thediscriminating means discriminates the disk set in the apparatus as adisk having two information faces when an amplitude of the focus errorsignal is lower than a prescribed level. Therefore, it is possible todiscriminate between a single-layer DVD and a double-layer DVD.

[0022] According to a ninth aspect of the present invention, there isprovided an optical disk apparatus comprising means for moving a focalpoint of a light beam for reproducing information recorded on aninformation face of a disk, in the direction perpendicular to theinformation face; means for detecting a reflected light from the disk;and means for discriminating whether the disk set in the apparatus is adisk having a thick base substrate or a disk having a thin basesubstrate on the basis of a maximum value of an amplitude of aninformation reproducing signal output from the reflected light detectingmeans when the focal point moving means is driven so that the focalpoint passes through the information face. Therefore, the discriminationbetween a DVD having a thin base substrate and a CD having a thick basesubstrate can be performed in a relatively simple structure.

[0023] According to a tenth aspect of the present invention, in theabove-mentioned apparatus, the information recorded in the disk isreproduced using an optical system for a disk having a thin basesubstrate. Therefore, when a disk having a thin base substrate is set inthe apparatus, the time interval before the reproduction of informationis reduced.

[0024] According to an eleventh aspect of the present invention, in theabove-mentioned apparatus, the moving speed of the focal point isreduced by controlling the focal point moving means when the output fromthe reflected light detecting means exceeds a prescribed level.Therefore, level changes of an AS1L signal, an ENV signal, and an FEsignal become gentle, and maximum values of amplitudes of these signalsare accurately detected, whereby the reliability of the diskdiscrimination is improved.

[0025] According to a twelfth aspect of the present invention, there isprovided an optical disk apparatus for reproducing information recordedon an information face of a disk using an optical head having a firstfocal point for reproducing a disk having a thick base substrate and asecond focal point for reproducing a disk having a thin base substrate,the apparatus comprising means for moving the first and second focalpoints in the direction perpendicular to the information face; means fordetecting a reflected light from the disk; a focus error detecting meansfor detecting a focused state of a light beam irradiating theinformation face, on the basis of an output signal from the reflectedlight detecting means; means for controlling focusing so that thefocused state of the light beam becomes a desired state, on the basis ofan output signal from the focus error detecting means; and means forgenerating a timing signal for driving the focusing control means on thebasis of an output signal from the focus error detecting means. In thisapparatus, the focal point moving means is driven so that the focalpoints go away from the disk, and the focusing control means is operatedin response to the timing signal. When no information is reproduced, thefocusing control means is immobilized, and the focal point moving meansis driven so that the focal points approach the disk, and the focusingcontrol means is operated in response to the timing signal. Therefore,even though the apparatus is not provided with a disk discriminatingmeans, the focusing control can be performed with focal points suitablefor the disk having a thick base substrate and the disk having a thinbase substrate, respectively. In addition, when a disk having athin-base substrate is set in the apparatus, the rise time of theapparatus can be reduced.

[0026] According to a thirteenth aspect of the present invention, thereis provided an optical disk apparatus for reproducing informationrecorded on an information face of a disk using an optical head having afirst focal point for reproducing a disk having a thick base substrateand a second focal point for reproducing a disk having a thin basesubstrate, the apparatus comprising means for moving the first andsecond focal points in the direction perpendicular to the informationface; means for detecting a reflected light from the disk; a focus errordetecting means for detecting a focused state of a light beamirradiating the information face on the basis of an output signal fromthe reflected light detecting means; means for controlling focusing sothat the focused state of the light beam becomes a desired state on thebasis of an output signal from the focus error detecting means; andmeans for generating a timing signal for driving the focusing controlmeans on the basis of an output signal from the focus error detectingmeans. In this apparatus, the focal point moving means is driven so thatthe focal points approach the disk, and the focusing control means isoperated in response to the timing signal. When no information isreproduced, the focusing control means is immobilized, and the focalpoint moving means is driven so that the focal points go away from thedisk, and the focusing control means is operated in response to thetiming signal. Therefore, even though the apparatus is not provided witha disk discriminating means, focusing control can be performed withfocal points suitable for the disk having a thick base substrate and thedisk having a thin base substrate, respectively. In addition, when adisk having a thick base substrate is set in the apparatus, the risetime of the apparatus can be reduced.

[0027] According to a fourteenth aspect of the present invention, thereis provided an optical disk apparatus for reproducing informationrecorded on an information face of a disk using an optical head having afirst focal point for reproducing a disk having a thick base substrateand a second focal point for reproducing a disk having a thin basesubstrate, this apparatus comprising means for moving the first andsecond focal points in the direction perpendicular to the informationface; means for detecting a reflected light from the disk; a focus errordetecting means for detecting a focused state of a light beamirradiating the information face on the basis of an output signal fromthe reflected light detecting means; means for controlling focusing sothat the focused state of the light beam becomes a desired state on thebasis of an output signal from the focus error detecting means; meansfor generating a timing signal for driving the focusing control means onthe basis of an output signal from the focus error detecting means; andmeans for discriminating whether the disk set in the apparatus is a diskhaving a thick base substrate or a disk having a thin base substrate. Inthis apparatus, when the disk set in the apparatus is discriminated as adisk having a thick base substrate, the focal point moving means isdriven so that the focal points approach the disk, and the focusingcontrol means is operated in response to the timing signal. Therefore,when a disk having a thick base substrate is set in the apparatus, thefocusing control can be performed with a focal point suitable for thedisk, and the rise time of the apparatus can be reduced.

[0028] According to a fifteenth aspect of the present invention, thereis provided an optical disk apparatus for reproducing informationrecorded on an information face of a disk using an optical head having afirst focal point for reproducing a disk having a thick base substrateand a second focal point for reproducing a disk having a thin basesubstrate, the apparatus comprising means for moving the first andsecond focal points in the direction perpendicular to the informationface; means for detecting a reflected light from the disk; a focus errordetecting means for detecting a focused state of a light beamirradiating the information face on the basis of an output signal fromthe reflected light detecting means; means for controlling focusing sothat the focused state of the light beam becomes a desired state on thebasis of an output signal from the focus error detecting means; meansfor generating a timing signal for driving the focusing control means onthe basis of an output signal from the focus error detecting means; andmeans for discriminating whether the disk set in the apparatus is a diskhaving a thick base substrate or a disk having a thin base substrate.When the disk set in the apparatus is discriminated as a disk having athin base substrate, the focal point moving means is driven so that thefocal points go away from the disk, and the focusing control means isoperated in response to the timing signal. Therefore, when a disk havinga thin base substrate is set in the apparatus, the focusing control canbe performed with a focal point suitable for the disk, and the rise timeof the apparatus can be reduced.

[0029] According to a sixteenth aspect of the present invention, thereis provided an optical disk apparatus for reproducing informationrecorded on an information face of a disk using an optical head having afirst focal point for reproducing a disk having a thick base substrateand a second focal point for reproducing a disk having a thin basesubstrate, the apparatus comprising means from moving the first andsecond focal points in the direction perpendicular to the informationface; means for detecting a reflected light from the disk; a focus errordetecting means for detecting a focused state of a light beamirradiating the information face, on the basis of an output signal fromthe reflected light detecting means; means for controlling focusing sothat the focused state of the light beam becomes a desired state on thebasis of an output signal from the focus error detecting means; meansfor generating a timing signal for driving the focusing control means onthe basis of an output signal from the focus error detecting means; andmeans for discriminating whether the disk set in the apparatus is a diskhaving a thick base substrate or a disk having a thin base substrate.When the disk set in the apparatus is discriminated as a disk having athick base substrate, the focal point moving means is driven so that thefocal points approach the disk, and the focusing control means isoperated in response to the timing signal. When the disk set in theapparatus is discriminated as a disk having a thin base substrate, thefocal point moving means is driven so that the focal points go away fromthe disk, and the focusing control means is operated in response to thetiming signal. Therefore, the focusing control can be performed withfocal points suitable for the disk having a thick base substrate and thedisk having a thin base substrate, respectively. In addition, the risetime of the apparatus can be reduced in both cases where a disk having athick base substrate is set and where a disk having a thin basesubstrate is set.

[0030] According to a seventeenth aspect of the present invention, thereis provided an optical disk apparatus for reproducing informationrecorded on an information face of a disk using an optical head having afirst focal point for reproducing a disk having a thick base substrateand a second focal point for reproducing a disk having a thin basesubstrate, the apparatus comprising means for moving the first andsecond focal points in the direction perpendicular to the informationface; means for detecting a reflected light from the disk, having afirst light responsive region that receives a center portion of thereflected light and a second light responsive region that receives aperipheral portion of the reflected light; and means for discriminatingwhether the disk set in the apparatus is a disk having a thick basesubstrate or a disk having a thin base substrate, on the basis ofsignals detected by the first and second light responsive regions whenthe focal point moving means is driven so that the first and secondfocal points pass through the information face. Therefore, thediscrimination between a disk having a thick base substrate and a diskhaving a thin base substrate can be performed.

[0031] According to an eighteenth aspect of the present invention, inthe above-mentioned apparatus, the discriminating means detects that afocal point of a light beam suitable for the disk is near theinformation face from the level of an information reproducing signaldetected by the reflected light detecting means, and then discriminateswhether the disk set in the apparatus is a disk having a thick basesubstrate or a disk having a thin base substrate on the basis of thesignals detected by the first and second light responsive regions.Therefore, the discrimination of the disk set in the apparatus isaccurately performed.

[0032] According to an nineteenth aspect of the present invention, inthe above-mentioned apparatus, the discriminating means detects that afocal point of a light beam suitable for the disk is near theinformation face on the basis of the ratio of a low frequency signallevel of the output signal from the reflected light detecting means tothe information reproducing signal level. Therefore, the discriminationof the disk can be performed accurately even when the reflectivity ofthe disk varies.

[0033] According to a twentieth aspect of the present invention, in theabove-mentioned apparatus, the discriminating means comprises means fordividing an amplitude of an information reproducing signal by a lowfrequency signal level of an output signal from the reflected lightdetecting means; and means for measuring an amount of light AS1Lpreceived by the first light responsive region, an amount of light AS2Lpreceived by the second light responsive region, and an amplitude ENVp ofthe information reproducing signal when a value obtained by the divisionattains a maximum value while driving the focal point moving means sothat the first and second focal points pass through the informationface. The discriminating means discriminates whether the disk set in theapparatus is a disk having a thick base substrate or a disk having athin base substrate on the basis of the ratio of AS1Lp×ENVp to AS2Lp.Therefore, the precision in the discrimination of the disk is improved.

[0034] According to a twenty-first aspect of the present invention, inthe above-mentioned apparatus, the discriminating means comprises meansfor adding an output signal from the first light responsive region to anoutput signal from the second light responsive region; means fordividing an amplitude of an information reproducing signal by a lowfrequency signal level of an output signal from the reflected lightdetecting means; and means for measuring a maximum value ASL_(max)obtained by the adding means and measuring an amount of light AS1Lpreceived by the first light responsive region, an amount of light AS2Lpreceived by the second light responsive region, and an amplitude ENVp ofthe information reproducing signal when a value obtained by the dividingmeans attains a maximum value while driving the focal point moving meansso that the first and second focal points pass through the informationface. The discriminating means discriminates whether the disk set in theapparatus is a disk having a thick base substrate or a disk having athin base substrate on the basis of the ratio of AS1Lp×ENVp toAS2Lp×ASL_(max). Therefore, the discrimination of the disk can beperformed accurately even when the reflectivity of the disk varies.

[0035] According to a twenty-second aspect of the present invention,there is provided an optical disk apparatus for reproducing informationrecorded on an information face of a disk using an optical head having afirst focal point for reproducing a disk having a thick base substrateand a second focal point for reproducing a disk having a thin basesubstrate, the apparatus comprising means for moving the first andsecond focal points in the direction perpendicular to the informationface; first and second light detecting means for detecting a reflectedlight from the disk, the second light detecting means receiving a largerportion of the reflected light than the first light detecting means; andmeans for discriminating whether the disk set in the apparatus is a diskhaving a thick base substrate or a disk having a think base substrate onthe basis of signals detected by the first and second light detectingmeans when the focal point moving means is driven so that the first andsecond focal points pass through the information face. Therefore, thediscrimination between a disk having a thick base substrate and a diskhaving a thin base substrate can be performed.

[0036] According to a twenty-third aspect of the present invention, inthe above-mentioned apparatus, the discriminating means detects that afocal point of a light beam suitable for the disk is near theinformation face from the level of information reproducing signalsdetected by the first and second light detecting means, and thendiscriminates whether the disk set in the apparatus is a disk having athick base substrate or a disk having a thin base substrate on the basisof signals detected by the first and second light receiving means.Therefore, the discrimination of the disk can be performed accurately.

[0037] According to a twenty-fourth aspect of the present invention, inthe above-mentioned apparatus, the discriminating means detects that afocal point of a light beam suitable for the disk is near theinformation face on the basis of the ratio of a low frequency signallevel in the output signals from the first and second light detectingmeans to the information reproducing signal level. Therefore, thediscrimination of the disk can be performed accurately even when thereflectivity of the disk varies.

[0038] According to a twenty-fifth aspect of the present invention, inthe above-mentioned apparatus, the discriminating means comprises meansfor dividing an amplitude of an information reproducing signal by a lowfrequency signal level of output signals from the first and second lightdetecting means; and means for measuring an amount of light AS1Lpreceived by the first light detecting means, an amount of light AS2Lpreceived by the second light detecting means, and an amplitude ENVp ofthe information reproducing signal when a value obtained by the divisionattains a maximum value while driving the focal point moving means sothat the first and second focal points pass through the informationface. The discriminating means discriminates whether the disk set in theapparatus is a disk having a thick base substrate or a disk having athin base substrate on the basis of the ratio of AS1Lp×ENVp to AS2Lp.Therefore, the precision in the discrimination of the disk is improved.

[0039] According to a twenty-sixth aspect of the present invention, inthe above-mentioned apparatus, the discriminating means comprises meansfor adding an output signal from the first light detecting means to anoutput signal from the second light detecting means; means for dividingan amplitude of an information reproducing signal by a low frequencysignal level of output signals from the first and second light detectingmeans; and means for measuring a maximum value ASL_(max) obtained by theadding means and measuring an amount of light AS1Lp received by thefirst light detecting means, an amount of light AS2Lp received by thesecond light detecting means, and an amplitude ENVp of the informationreproducing signal when a value obtained by the dividing means attains amaximum value while driving the focal point moving means so that thefirst and second focal points pass through the information face. Thediscriminating means discriminates whether the disk set in the apparatusis a disk having a thick base substrate or a disk having a thin basesubstrate on the basis of the ratio of AS1Lp×ENVp to AS2Lp×ASL_(max).Therefore, the discrimination of the disk can be performed accuratelyeven when the reflectivity of the disk varies.

[0040] According to a twenty-seventh aspect of the present invention,there is provided an optical disk apparatus for reproducing both a diskhaving one information face and a disk having two information faces byirradiating the disk with a focused light beam, the apparatus comprisingmeans for moving a focal point of the light beam in the directionperpendicular to the information face; means for detecting a reflectedlight from the disk, having a first light responsive region thatreceives a center portion of the reflected light and a second lightresponsive region that receives a peripheral portion of the reflectedlight; and means for discriminating whether the disk set in theapparatus is a disk having one information face or a disk having twoinformation faces on the basis of signals detected by the first andsecond light responsive regions when the focal point moving means isdriven so that the focal point passes through the information face.Therefore, the discrimination between a disk having one information faceand a disk having two information faces can be performed.

[0041] According to a twenty-eighth aspect of the present invention, inthe above-mentioned apparatus, the discriminating means detects that thefocal point of the light beam is near the information face from thelevel of an information reproducing signal detected by the reflectedlight detecting means, and then discriminates whether the disk set inthe apparatus is a disk having one information face or a disk having twoinformation faces on the basis of the signals detected by the first andsecond light responsive regions. Therefore, the discrimination of thedisk can be performed accurately.

[0042] According to a twenty-ninth aspect of the present invention, inthe above-mentioned apparatus, the discriminating means detects that thefocal point of the light-beam is near the information face on the basisof the ratio of a low frequency signal level of the output signal fromthe reflected light detecting means to the information reproducingsignal level. Therefore, the discrimination of the disk can be performedaccurately even when the reflectivity of the disk varies.

[0043] According to a thirtieth aspect of the present invention, in theabove-mentioned apparatus, the discriminating means comprises means fordividing an amplitude of an information reproducing signal by a lowfrequency signal level of an output signal from the reflected lightdetecting means; and means for measuring an amount of light AS1Lpreceived by the first light responsive region, an amount of light AS2Lpreceived by the second light responsive region, and an amplitude ENVp ofthe information reproducing signal when a value obtained by the divisionattains a maximum value while driving the focal point moving means sothat the focal point passes through the information face. Thediscriminating means discriminates whether the disk set in the apparatusis a disk having one information face or a disk having two informationfaces on the basis of the ratio of AS1Lp×ENVp to AS2Lp. Therefore, theprecision in the discrimination of the disk is improved.

[0044] According to a thirty-first aspect of the present invention, inthe above-mentioned apparatus, the discriminating means comprises meansfor adding an output signal from the first light responsive region to anoutput signal from the second light responsive region; means fordividing an amplitude of an information reproducing signal by a lowfrequency signal level of an output signal from the reflected lightdetecting means; and means for measuring a maximum value ASL_(max)obtained by the adding means and measuring an amount of light AS1Lpreceived by the first light responsive region, an amount of light AS2Lpreceived by the second light responsive region, and an amplitude ENVp ofthe information reproducing signal when a value obtained by the dividingmeans attains a maximum value while driving the focal point moving meansso that the focal point passes through the information face. Thediscriminating means discriminates whether the disk set in the apparatusis a disk having one information face or a disk having two informationfaces on the basis of the ratio of AS1Lp×ENVp to AS2Lp×ASL_(max).Therefore, the discrimination of the disk can be performed accuratelyeven when the reflectivity of the disk varies.

[0045] According to a thirty-second aspect of the present inventionthere is provided an optical disk apparatus for reproducing both a diskhaving one information face and a disk having two information faces byirradiating the disk with a focused light beam, the apparatus comprisingmeans for moving a focal point in the direction perpendicular to theinformation face; first and second light detecting means for detecting areflected light from the disk, the second light detecting meansreceiving a larger portion of the reflected light than the first lightdetecting means; and means for discriminating whether the disk set inthe apparatus is a disk having one information face or a disk having twoinformation faces on the basis of signals detected by the first andsecond light detecting means when the focal point moving means is drivenso that the focal point passes through the information face. Therefore,the discrimination between a disk having one information face and a diskhaving two information faces can be performed.

[0046] According to a thirty-third aspect of the present invention, inthe above-mentioned apparatus, the discriminating means detects that thefocal point of the light beam is near the information face, from thelevel of information reproducing signals detected by the first andsecond light detecting means, and then discriminates whether the diskset in the apparatus is a disk having one information face or a diskhaving two information faces on the basis of signals detected by thefirst and second light receiving means. Therefore, the discrimination ofthe disk can be performed accurately.

[0047] According to a thirty-fourth aspect of the present invention, inthe above-mentioned apparatus, the discriminating means detects that thefocal point of the light beam is near the information face on the basisof the ratio of a low frequency signal level in the output signals fromthe first and second light detecting means to the informationreproducing signal level. Therefore, the discrimination of the disk canbe performed accurately even when the reflectivity of the disk varies.

[0048] According to a thirty-fifth aspect of the present invention, inthe above-mentioned apparatus, the discriminating means comprises meansfor dividing an amplitude of an information reproducing signal by a lowfrequency signal level of output signals from the first and second lightdetecting means; and means for measuring an amount of light AS1Lpreceived by the first light detecting means, an amount of light AS2Lpreceived by the second light detecting means, and an amplitude ENVp ofthe information reproducing signal when a value obtained by the divisionattains a maximum value while driving the focal point moving means sothat the focal point passes through the information face. Thediscriminating means discriminates whether the disk set in the apparatusis a disk having one information face or a disk having two informationfaces on the basis of the ratio of AS2Lp×ENVp to AS2Lp. Therefore, theprecision in the discrimination of the disk can be improved.

[0049] According to a thirty-sixth aspect of the present invention, inthe above-mentioned apparatus, the discriminating means comprises meansfor adding an output signal from the first light detecting means to anoutput signal from the second light detecting means; means for dividingan amplitude of an information reproducing signal by a low frequencysignal level of output signals from the first and second light detectingmeans; and means for measuring a maximum value ASL_(max) obtained by theadding means and measuring an amount of light AS1Lp received by thefirst light detecting means, an amount of light AS2Lp received by thesecond light detecting means, and an amplitude ENVp of the informationreproducing signal when a value obtained by the dividing means attains amaximum value while driving the focal point moving means so that thefocal point passes through the information face. The discriminatingmeans discriminates whether the disk set in the apparatus is a diskhaving one information face or a disk having two information faces onthe basis of the ratio of AS1Lp×ENVp to AS2Lp×ASL_(max). Therefore, thediscrimination of the disk can be performed accurately even when thereflectivity of the disk varies.

[0050] According to a thirty-seventh aspect of the present invention,there is provided an optical disk apparatus for reproducing informationrecorded on an information face of a disk using an optical head having afirst focal point for reproducing a disk having a thick base substrateand a second focal point for reproducing a disk having a thin basesubstrate, the apparatus comprising means for moving the first andsecond focal points in the direction perpendicular to the informationface; means for detecting a reflected light from the disk; means fordiscriminating whether the disk set in the apparatus is a disk having athick base substrate or a disk having a thin base substrate; and aninformation face detecting means for detecting that a focal point of alight beam suitable for the disk is near the information face, from anoutput signal of the reflected light detecting means, while driving thefocal point moving means so that the first and second focal points passthrough the information face. In this apparatus, the discriminatingmeans discriminates whether the disk set in the apparatus is a diskhaving a thick base substrate or a disk having a thin base substrate onthe basis of the ratio of a maximum value ASL_(max) of a signal outputfrom the reflected light detecting means to a level ASLp of a signaloutput from the reflected light detecting means when the informationface is detected by the information face detecting means, while drivingthe focal point moving means so that the first and second focal pointspass through the information face. Therefore, the discrimination betweena disk having a thick base substrate and a disk having a thin basesubstrate can be performed.

[0051] According to a thirty-eighth aspect of the present invention, inthe above-mentioned apparatus, the information face detecting meansdetects that a focal point of a light beam suitable for the disk is nearthe information face on the basis of the ratio of a low frequency signallevel of an output signal from the reflected light detecting means to aninformation reproducing signal level of the output signal. Therefore,the discrimination of the disk can be performed accurately even when thereflectivity of the disk varies.

[0052] According to a thirty-ninth aspect of the present invention,there is provided an optical disk apparatus for reproducing informationrecorded on an information face of a disk using an optical head having afirst focal point for reproducing a disk having a thick base substrateand a second focal point for reproducing a disk having a thin basesubstrate, the apparatus comprising means for moving the first andsecond focal points in the direction perpendicular to the informationface; means for detecting a reflected light from the disk; and means fordiscriminating whether the disk set in the apparatus is a disk having athick base substrate or a disk having a thin base substrate. In thisapparatus, a maximum value AS1L_(max) of an output from the reflectedlight detecting means and a maximum value ENV_(max) of an amplitude ofan information reproducing signal are measured while driving the focalpoint moving means so that the first and second focal points passthrough the information face, and the discriminating means discriminateswhether the disk set in the apparatus is a disk having a thick basesubstrate or a disk having a thin base substrate on the basis of theratio of ENV_(max) to AS1L_(max). Therefore, the discrimination betweena disk having a thick base substrate and a disk having a thin basesubstrate can be performed.

[0053] According to a fortieth aspect of the present invention, there isprovided an optical disk apparatus for reproducing information recordedon an information face of a disk using an optical head having a firstfocal point for reproducing a disk having a thick base substrate and asecond focal point for reproducing a disk having a thin base substrate,the apparatus comprising means for moving the first and second focalpoints in the direction perpendicular to the information face; means fordetecting a reflected light from the disk; a focus error detecting meansfor detecting focused state of a light beam irradiating the informationface on the basis of an output signal from the reflected light detectingmeans; means for controlling focusing so that the focused state of thelight beam becomes a desired state on the basis of an output signal fromthe focus error detecting means, the focusing control means including anamplifier having a variable amplification factor and amplifying theoutput signal from the focus error detecting means; and an informationface detecting means for detecting that a focal point of a light beamsuitable for the disk is near the information face, from an outputsignal of the reflected light detecting means. In this apparatus, theamplification factor of the amplifier is set on the basis of an outputvalue from the reflected light detecting means when the information facedetecting means outputs an information face detecting signal, whiledriving the focal point moving means so that the first and second focalpoints pass through the information face. Therefore, even when thereflectivity of the disk varies, the amplitude of the FE signal isconstant, whereby an accurate timing for performing the focusing controlis obtained.

[0054] According to a forty-first aspect of the present invention, inthe above-mentioned apparatus, after setting the amplification factor ofthe amplifier, the focusing control means is operated by detecting thatan output signal from the amplifier reaches a prescribed value.Therefore, the focusing control is avoided from being performed at awrong timing due to noise or the like.

[0055] According to a forty-second aspect of the present invention, inthe above-mentioned apparatus, the information face detecting meansdetects that a focal point of a light beam suitable for the disk is nearthe information face on the basis of the ratio of a low frequency signallevel of an output signal from the reflected light detecting means to aninformation reproducing signal level of the output signal. Therefore,even when the reflectivity of the disk varies, the presence of thesuitable focal point in the vicinity of the information face can bedetected at an accurate timing.

[0056] According to a forty-third aspect of the present invention, inthe above-mentioned apparatus, the discrimination of the disk set in theapparatus is performed after the focal point passes through theinformation face twice. Therefore, the detection of the reflected lightis accurately performed, whereby the precision in the discrimination ofthe disk is improved.

[0057] According to a forty-fourth aspect of the present invention, inthe above-mentioned apparatus, the focal point is slightly moved in thedirection perpendicular to a track on the disk during a period of timewhen the focal point is passed through the information face bycontrolling the focusing control means. Therefore, it is avoided thatthe focal point is always positioned between tracks, whereby theprecision in the discrimination of the disk is improved.

[0058] According to a forty-fifth aspect of the present invention, inthe above-mentioned apparatus, the moving speed of the focal point isreduced by controlling the focal point moving means when an output valuefrom the reflected light detecting means exceeds a prescribed value.Therefore, the change of the reflected light amount becomes gentle, andthe signal level is accurately detected, whereby the precision in thediscrimination of the disk is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0059]FIG. 1 is a block diagram illustrating an optical disk apparatusin accordance with a first embodiment of the present invention.

[0060] FIGS. 2(a)-2(d) are waveforms of an FE signal, an AS1 signal, anAS1L signal, and an ENV signal, respectively, and FIG. 2(e) illustratesa position of a focal point F, according to the first embodiment of theinvention.

[0061] FIGS. 3(a)-3(d) are waveforms of ENV signals and AS1L signals ina single-layer DVD, a double-layer DVD, a CD, and a CDR, respectively,for explaining a disk discriminating process according to the firstembodiment of the invention.

[0062]FIG. 4 is a block diagram illustrating an optical disk apparatusin accordance with a second embodiment of the present invention.

[0063]FIG. 5 is a block diagram illustrating an optical disk apparatusin accordance with a modification of the second embodiment of theinvention.

[0064]FIG. 6 is a block diagram illustrating an optical disk apparatusin accordance with a third embodiment of the present invention.

[0065]FIG. 7 is a schematic diagram illustrating an optical systemhaving two focal points according to the third embodiment of theinvention.

[0066] FIGS. 8(a)-8(c) are waveforms of FE signals and ENV signals in asingle-layer DVD, a double-layer DVD, and a CD, respectively, accordingto the third embodiment of the invention.

[0067] FIGS. 9(a)-9(d) are waveforms of ENV signals and AS1L signals ina single-layer DVD, a double-layer DVD, a CD, and a CD-R, respectively,for explaining a disk discriminating process according to the thirdembodiment of the invention.

[0068]FIG. 10 is a block diagram illustrating an optical disk apparatusin accordance with a fourth embodiment of the present invention.

[0069]FIG. 11 is an schematic diagram illustrating a photodetectorincluded in the apparatus according to the fourth embodiment of theinvention.

[0070]FIG. 12 is a flow chart for explaining the operation of theapparatus according to the fourth embodiment of the invention.

[0071] FIGS. 13(a)-13(c) are waveforms of FE signals, ENV signals, AS1Lsignals, ASL signals, and ENV/ASL values, in a single-layer DVD, adouble-layer DVD, and a CD, respectively, according to the fourthembodiment of the invention.

[0072]FIG. 14 is a flow chart for explaining a disk discriminatingprocess according to the fourth embodiment of the invention.

[0073]FIG. 15 is a flow chart for explaining a disk discriminatingprocess according to the fourth embodiment of the invention.

[0074] FIGS. 16(a) and 16(b) are waveforms for explaining a movement ofa focusing lens for a DVD and a CD, respectively, according to thefourth embodiment of the invention.

[0075]FIG. 17 is a waveform of an FE signal for explaining the operationof an amplifier according to the fourth embodiment of the invention.

[0076]FIG. 18 is a block diagram illustrating an optical disk apparatusemploying two photodetectors, according to a modification of the fourthembodiment of the invention.

[0077] FIGS. 19(a) and 19(b) are schematic diagrams illustrating thephotodetectors shown in FIG. 18.

[0078]FIG. 20 is a block diagram illustrating an optical disk apparatusin accordance with a fifth embodiment of the present invention.

[0079] FIGS. 21(a) and 21(b) are waveforms illustrating a movement of afocusing lens and an FE signal, respectively, and

[0080] FIGS. 21(c) and 21(d) are block diagrams illustrating a signalprocessing circuit and a CD information reproducing circuit,respectively, according to the fifth embodiment of the invention.

[0081] FIGS. 22(a) and 22(b) are waveforms illustrating a movement of afocusing lens and an FE signal, respectively, according to the fifthembodiment of the invention.

[0082]FIG. 23 is a diagram for explaining relationships between the Zvalue and the disk discrimination according to the third embodiment ofthe invention.

[0083] FIGS. 24(a) and 24(b) are diagrams illustrating positionalrelationships between the information face and focal points F_(DVD) andF_(CD), and reflected beams from the information face to aphotodetector, respectively, when ENV/ASL attains a maximum value,according to the fourth embodiment of the invention.

[0084]FIG. 25 is a schematic diagram illustrating a conventional CD.

[0085]FIG. 26 is a schematic diagram illustrating a typical double-layerDVD.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0086] [Embodiment 1]

[0087]FIG. 1 is a block diagram illustrating an optical disk apparatusin accordance with a first embodiment of the present invention.

[0088] The optical disk apparatus according to this first embodiment ofthe invention can identify whether a disk set in the apparatus is asingle-layer DVD, a double-layer DVD, a CD, or a CD-R. In FIG. 1, when adisk 100 is put on a tray 149, a microcomputer 147 drives a motor 118 tomove the tray 149 so that the disk 100 is fixed to a rotation axis 102of the motor 101.

[0089] Reference numeral 104 designates a transport stage. On thetransport stage 104, a 650 nm laser 105, a coupling lens 106, apolarization beam splitter 107, a ¼ wavelength plate 108, a totallyreflecting mirror 109, a photodetector 111, a motor 128, and actuators112 and 127 are fixed. The transport stage 104 is movable in the radialdirection of the disk 100, and the movement is controlled by a transportmotor 103, such as a linear motor.

[0090] A light beam emitted from the laser 105 on the transport stage104 is converted to a parallel light beam by the coupling lens 106. Theparallel light beam travels through the polarization beam splitter 107and the ¼ wavelength plate 108 and is reflected by the totallyreflecting mirror 109. The reflected light is conversed by the focusinglens 110 on an information surface of the disk 100. The focusing lens110 and the actuator 112 are used when a DVD is reproduced. When a CD isreproduced, the focusing lens 110 b and the actuator 112 for the DVD arechanged to the focusing lens 126 and the actuator 127 for the CD by themotor 128. Although the CD is reproduced using a 780 nm laser in aconventional apparatus for reproducing the CD only, in the optical diskapparatus shown in FIG. 1 the 650 nm laser 105 is employed and thefocusing lens 126 for the CD is designed with regard to this wavelength(650 nm) and the base material thickness of the CD (1.2 mm).

[0091] The light beam reflected by the information surface of the disk100 travels through the focusing lens 110 and is reflected by thetotally reflecting mirror 109. The reflected light travels through the ¼wavelength plate 108, the polarization beam splitter 107, the detectorlens 113, and the cylindrical lens 116, and irradiates the photodetector111 that is divided into four. The focusing lens 110 is fixed to amoving part of the actuator 112. The actuator 112 is composed of a coilfor focusing, a coil for tracking, a permanent magnet for focusing, anda permanent magnet for tracking (these elements are not shown in thefigure) Therefore, when a voltage is applied to the focusing coil of theactuator 112 using a power amplifier 133, a current flows through thiscoil and a magnetic force is applied to this coil from the permanentmagnet for focusing, whereby the focusing lens 110 moves in thedirection perpendicular to the surface of the disk 100. In the figure,the lens 110 moves up and down. In this way, the focusing lens 110 iscontrolled so that the focal point of the light beam is alwayspositioned on the information surface of the disk 100 in response to afocusing error signal that represents an error between the focal pointof the light beam and the information surface of the disk.

[0092] When a voltage is applied to the tracking coil of the actuator112 using a power amplifier 136, a current flows through this coil and amagnetic force is applied to this coil from the permanent magnet fortracking, whereby the focusing lens 110 moves in the radial direction ofthe disk 100, i.e., the direction transverse to the track on the disk100. In the figure, the lens 110 moves right and left.

[0093] The light beam reflected by the disk 100 and applied to thephotodetector 111 is converted to current by the photodetector ill thatis divided into four and is inputted to I/V converters 114, 115, 119,and 120. Each I/V converter converts the inputted current into a voltagein response to the current level. Voltage signals outputted from the I/Vconverters 114, 115, 119, and 120 are inputted to adders 121, 122, 123,and 124 in such a manner that two of the signals outputted from the I/Vconverters are inputted to each adder. Each adder adds the inputted twosignals. Signals outputted from the adders 121, 122, 123, and 124 areinputted to differential amplifiers 125 and 117 in such a manner thattwo of the signals outputted from the adders are inputted to eachdifferential amplifier. The differential amplifier 117 receives signalsoutputted from the adders 123 and 124 and calculates a differencebetween these signals.

[0094] The optical system shown in FIG. 1 constitutes a focusing errordetection system that is generally called an astigmatic method. So, anoutput from the differential amplifier 117 becomes a focusing errorsignal (hereinafter referred to as an FE signal) that represents anerror between the focal point of the light beam 150 and the informationsurface of the disk 100. This FE signal is transmitted through a phasecompensator 130, a switch 131, and an adder 132 to the power amplifier133, and a voltage is applied to the focusing coil (not shown) of theactuator 112 by the power amplifier 133. The phase compensator 130 makesthe focusing control system stable. In this way, the focal point of thelight beam is always positioned on the information surface of the disk100 by moving, in response to the FE signal, the focusing lens 110 orthe focusing lens 126 when the focusing lens 110 is changed to thefocusing lens 126.

[0095] The differential amplifier 125 receives signals outputted fromthe adders 121 and 122 and calculates a difference between thesesignals. The optical system shown in FIG. 1 constitutes a tracking errordetection system that is generally called a push-pull method. Therefore,an output from the differential amplifier 125 becomes a tracking errorsignal (hereinafter referred to as a TE signal) that represents an errorbetween the focal point of the light beam 150 and the track on the disk100. This TE signal is transmitted through a switch 134 and a phasecompensator 135 to the power amplifier 136, and an output from the poweramplifier 136 is applied to the tracking coil (not shown) of theactuator 112 as a voltage. The phase compensator 135 makes the trackingcontrol system stable. In this way, the focal point of the light beam isalways positioned on the track of the disk 100 by moving the focusinglens 110 or the focusing lens 126 in response to the TE signal.

[0096] An output from an adder 148 is a signal obtained by adding allthe signals outputted from the photodetector 111, and this signal showsan amount of totally reflected light from the disk 100. Hereinafter,this signal is called an AS1 signal. This AS1 signal changes accordingto the presence and absence of the pits on the disk. This AS1 signalshowing the amount of totally reflected light is sent to an envelopedetector 143 and to a signal processing circuit (not shown) fordemodulating information.

[0097] The envelope detector 143 outputs a signal level of an ACcomponent produced by the pits on the disk. Hereinafter, this outputsignal is called an ENV signal. A low pass filter 165 (hereinafterreferred to as LPF) eliminates the AC component from the AS1 signal, andan AS1 signal passing through the LPF 165 is called an AS1L signal. TheAS1L signal, the ENV signal, and the FE signal are converted to digitalsignals by A/D (analog to digital) converters 142, 144, and 140,respectively, and are sent to the microcomputer 147.

[0098] A description is now given of the operation of the optical diskapparatus shown in FIG. 1.

[0099] When the disk 100 is put on the tray 149, the microcomputer 147drives the motor 118 so that the disk 100 is fixed to the rotation axis102 of the motor 101. Next, the microcomputer 147 sets a prescribedvalue in a D/A (digital to analog) converter 145 to drive the transportmotor 103 through the power amplifier 139 so that the transport stage104 moves toward the inner circumference of the disk 100, and drives themotor 128 to select the focusing lens 110 and the actuator 112 for theDVD.

[0100] Further, the microcomputer 147 rotates the motor 101. Therotating speed of the motor 101 is set at a rotating speed normalizedfor reproduction of information on an inner circumference of a DVD. Whenthe motor 101 reaches the rotating speed, the motor 101 sends an OKsignal to a terminal a of the microcomputer 147. Receiving the OKsignal, the microcomputer 147 sends a command through a terminal b to alaser driving circuit 129 so as to make the laser 105 emit light.Meanwhile, the microcomputer 147 sets a radiant intensity of the laser105, through a D/A converter 146, in the laser driving circuit 129. Thisradiant intensity must be sufficiently low so that the informationrecorded in the disk 100 is not destroyed when the disk 100 is a CD-R.

[0101] Further, the microcomputer 147 sets a prescribed value in a D/Aconverter 141 to drive the focusing lens 110 through the adder 132 andthe power amplifier 133 so that the focusing lens 110 moves oncedownward and then gradually upward, that is, once away from the disk 100and then toward the disk 100. At this time, the switches 131 and 134 areopen so that the focusing coil and tracking coil of the actuator 112 arenot driven in response to the FE signal and the TE signal. Thereafter,the microcomputer 147 receives the FE signal, the AS1L signal, and theENV signal through the AID converters 140, 142, and 144, respectively,while the focusing lens 110 moves, and the microcomputer 147 identifieswhether the disk 100 set in the apparatus is a single-layer DVD, adouble-layer DVD, a CD, or a CD-R on the basis of the FE signal, theAS1L signal, and the ENV signal.

[0102] When the disk 100 is identified as a CD-R, since there is therisk of destruction of information recorded on the disk 100, themicrocomputer 147 drives the motor 118 to move the tray 149 so that thedisk 100 is ejected from the apparatus. When the disk 100 is identifiedas a CD, the microcomputer 147 drives the motor 128 to change theactuator 112 and the focusing lens 110 to the actuator 127 and thefocusing lens 126 for the CD.

[0103] Next, the microcomputer 147 controls the laser driving circuit129 to set the radiant intensity of the laser 105 at an appropriatevalue for the disk 100, i.e., a CD or a DVD. Thereafter, themicrocomputer 147 sets the output from the D/A converter 141 at zero andcloses the switches 131 and 134 to make loops. Using the loops, themicrocomputer 147 controls the actuator 112 with outputs from the poweramplifiers 133 and 136 to perform focusing and tracking, respectively,whereby information recorded on the disk 100 is reproduced.

[0104] The discrimination of the disk using the microcomputer 147 isperformed only when a disk 110 is newly fixed to the rotation axis 102of the motor 101. In the case where reproduction of information in thedisk is halted temporarily and then started again, discrimination of thedisk is not performed. Therefore, the rising time when the reproductionis started again can be reduced.

[0105] A description is now given of the FE signal, the AS1 signal, theAS1L signal, and the ENV signal.

[0106] FIGS. 2(a), 2(b), 2(c), and 2(d) show waveforms of the FE signal,the AS1 signal, the AS1L signal, and the ENV signal, respectively, whenthe focusing lens 110 gradually moves upward in the case where asingle-layer DVD is set in the optical disk apparatus. FIG. 2(e) showsthe position of the focal point F. In these figures, the ordinate showsthe signal level, and the abscissa shows time. The FE signal, the AS1signal, the AS1L signal, and the ENV signal vary when the focal point ofthe light beam irradiating the disk passes through the informationsurface, i.e., the Al reflecting film. The FE signal becomes 0 at thetime t1 when the focal point of the light beam is on the informationsurface of the disk. The waveform of the FE signal, when the focal pointof the light beam passes through the information surface of the disk, isgenerally called a S curve. The AS1 signal gradually increases as thefocal point of the light beam approaches the information surface of thedisk and gradually decreases as the focal point goes away from theinformation surface. In addition, the AS1 signal changes according tothe presence and absence of the pits on the disk. The AS1L signal is asignal obtained by averaging the level changes of the AS1 signal due tothe pits on the disk. The ENV signal is a signal showing the levelchange of the amount of the reflected light due to the presence andabsence of the pits on the disk. The position of the focal point F ofthe light beam shown in FIG. 2(e) is determined by the signal leveloutputted from the microcomputer 147 and inputted to the D/A converter141.

[0107] As shown in FIG. 2(e), the microcomputer 147 moves the focalpoint F of the light beam slowly in the period from t0 to t2 because theslow movement of the focal point makes the change of the signal levelgentle, whereby accurate measurement of the respective signals ispossible. In the period from t0 to t2, the AS1L signal exceeds areference value w because, in this period, the focal point of the lightbeam is in the vicinity of the information surface of the disk.Therefore, in the period from t0 to t2, the focal point F of the lightbeam is moved slowly to measure the respective signals accurately,whereby the time required for discriminating the disk is reduced.

[0108] Next, a method of discriminating the disk using the microcomputer147 in response to the FE signal, the AS1L signal, and the ENV signalwill be described.

[0109] The microcomputer 147 calculates the maximum values of the FEsignal, the AS1L signal, and the ENV signal. FIGS. 3(a), 3(b), 3(c), and3(d) show waveforms of the ENV signal and the AS1L signal when thefocusing lens 110 gradually moves upward, for a single-layer DVD (DVD1),a double-layer DVD (DVD2), a CD, and a CD-R, respectively. In thesefigures, the ordinate shows the signal level, and the abscissa showstime.

[0110] In FIG. 3(a), Kenv and Kas show the maximum values of the ENVsignal and the AS1L signal, respectively, within a period of time wherethe focusing lens 110 moves. Likewise, Lenv and Las in FIG. 3(b), Menvand Mas in FIG. 3(c), and Nenv and Nas in FIG. 3(d) show the maximumvalues.

[0111] The level of the ENV signal and the level of the AS1L signalattain maximum values in the single-layer DVD and minimum values in theCD-R. The level of the ENV signal and the level of the AS1L signal inthe double-layer DVD are lower than those in the single-layer DVDbecause the reflectivity of the first layer of the double-layer DVD(about 35%) is lower than the reflectivity of the single-layer DVD(about 90%).

[0112] Further, the ENV signal level Menv in the CD is lower than theENV signal levels Kenv and Lenv in the single-layer DVD and thedouble-layer DVD because the ENV signal in the CD is measured using theoptical system for the DVD.

[0113] Furthermore, differences in the ENV signal levels (Menv and Nenv)and in the AS1L signal levels (Mas and Nas) between the CD and the CD-Rare attributed to the fact that the absorptivity of the CD-R for 650 nmlight is higher than that of the CD.

[0114] The microcomputer 147 stores Pas that satisfies therelationships, NAS<Pas<Mas, Nas<Pas<Las, and Nas<Pas<Kas, and comparesthe maximum value of the AS1L signal with Pas after the calculation ofthe maximum values of the FE signal, the AS1L signal, and the ENVsignal. When the maximum value of the AS1L signal is lower than Pas, themicrocomputer 147 identifies the disk in the apparatus as a CD-R. Inthis case, the microcomputer 147 drives the motor 118 to move the tray149 so that the disk 100, i.e., the CD-R, is ejected from the apparatus.

[0115] Next, the microcomputer 147 calculates Kenv/Kas, Lenv/Las,Menv/Mas, and Nenv/Nas. The object of this division of the maximum valueof the ENV signal by the maximum value of the AS1L signal is to absorbinfluences on the maximum value of the ENV signal due to variations inthe reflectivity of the disk 100 or in the radiant intensity of thelaser 105. According to an experiment, this value is about 6 in the DVD(single-layer DVD and the double-layer DVD) and about 2 in the CD.Therefore, when this value is larger than 4, the microcomputer 147identifies the disk set in the apparatus as a DVD. When this value islower than 4, the disk is identified as a CD. However, since the resultof the division changes when the amplification factors of the AS1Lsignal and the ENV signal change, the value for comparison must bechanged according to the amplification factors.

[0116] When the disk set in the optical disk apparatus is identified asa CD, the microcomputer 147 drives the motor 128 to change the actuator112 and the focusing lens 110 to the actuator 127 and the focusing lens126 for the CD.

[0117] When the disk set in the apparatus is identified as a DVD, themicrocomputer 147, which stores Qenv that satisfies the relationship ofLenv<Qenv<Kenv, compares the measured ENV signal with Qenv. According tothe result of the comparison, the microcomputer 147 performs thediscrimination between a single-layer DVD and a double-layer DVD.

[0118] Although the discrimination between a single-layer DVD and adouble-layer DVD is performed using the maximum value of the ENV signalin this first embodiment of the invention, it may be performed using themaximum amplitude of the FE signal or the maximum value of the AS1Lsignal because there is a difference in the amplitude level of the FEsignal or the AS1L signal level between the single-layer DVD and thedouble-layer DVD due to the difference in reflectivities between theseDVDS.

[0119] Further, although the discrimination of the CD-R is performedusing the AS1L signal level in this first embodiment of the invention,it may be performed using the FE signal level or the ENV signal levelbecause the FE signal level and the ENV signal level in the CD-R arelower than those in the CD due to the difference in absorptivitiesbetween the CD-R and the CD. In this first embodiment of the invention,the discrimination between a CD and a DVD is performed on the basis ofthe value obtained by dividing the maximum value of the ENV signal bythe maximum value of the AS1L signal. According to the experiment-, themaximum value of the ENV signal in the double-layer DVD, which ismeasured with the lens for the DVD, is larger than the maximum value ofthe ENV signal in the CD, which becomes small because it is measuredwith the lens for the DVD though it should be measured with the lens forthe CD. So, it is possible to identify whether the disk in the apparatusis a single-layer DVD, a double-layer DVD, a CD, or a CD-R on the basisof the maximum value of the ENV signal. More specifically, thediscrimination between a single-layer DVD and a double-layer DVD isperformed using a difference in the reflectivities, and thediscrimination between a DVD and a CD is performed using a difference indetected output signals caused by that an optimum detection lens for thesubstrate thickness is not used. Further, the discrimination between aCD and a CD-R is performed using a difference in the absorptivities.When the discrimination is performed on the basis of the maximum valueof the ENV signal, since the division is not necessary, the processingof the microcomputer 147 is simplified.

[0120] In this first embodiment of the invention, the radiant intensityof the laser 105 is maintained low so that the information on the diskis not destroyed when the disk is a CD-R. However, after it is found bythe first vertical movement of the focusing lens 110 that the disk isnot a CD-R, the radiant intensity of the laser 105 may be increased andthe focusing lens 110 is moved again to identify whether the disk is aDVD or a CD. Since the level of the detected signal can be made higherthan noise level by increasing the radiant level of the laser, theprecision in the discrimination is significantly improved.

[0121] Although the discrimination of the disk is performed using theoptical system for the DVD, it may be performed using the optical systemfor the CD. In this case, however, since the high-low relationships ofthe ENV signal and the FE signal are inverted, the conditions for thediscrimination must be changed.

[0122] Further, in this first embodiment of the invention, the focusinglens 110 once moves downward and then gradually approaches the disk 100and, during the approach of the lens 110 to the disk 100, the FE signal,the ENV signal, and the AS1L signal are measured. However, these signalsmay be measured when the focusing lens 110 gradually moves downward awayfrom the disk 100.

[0123] As described above, according to the first embodiment of thepresent invention, the maximum values of the AS1L signal and the ENVsignal are measured, and the maximum value of the ENV signal is dividedby the maximum value of the AS1L signal and, thereafter, the result iscompared with a predetermined reference value. Therefore, it is possibleto discriminate between a DVD having a thin base substrate and a CDhaving a thick base substrate.

[0124] Since the maximum value of the AS1L signal is compared with aprescribed reference value, the discrimination of a CD-R is performedwith a simple structure.

[0125] Since the discrimination of the disk is performed with a lightbeam having an intensity lower than that for reproducing information,even when the disk set in the apparatus is a CD-R, information recordedin the CD-R is not destroyed.

[0126] Since the maximum value of the ENV signal amplitude is comparedwith a prescribed reference value, the discrimination between asingle-layer DVD and a double-layer DVD is performed with a simplestructure.

[0127] Since the maximum value of the ENV signal amplitude is comparedwith a prescribed reference value, the discrimination between the DVDhaving a thin base substrate and the CD having a thick base substrate isperformed with a simple structure.

[0128] Since the discrimination of the disk is performed using theoptical system for the disk having a thin base substrate, when the diskhaving a thin base substrate is set in the apparatus, the time intervalrequired before reproduction of information in the disk is reduced.

[0129] Since the moving speed of the focusing lens 110 is reduced whenthe level of the AS1L signal exceeds the reference value W, the levelchange of the AS1L signal, the ENV signal, and the FE signal becomesgentle. Therefore, the microcomputer 147 can receive accurate maximumvalues of the amplitudes of the AS1L signal, the ENV signal, and the FEsignal, whereby the discrimination of the disk is performed with highreliability.

[0130] Although the discrimination of the CD-R is performed using themaximum value of the AS1L signal in this first embodiment of theinvention, it may be performed using the maximum amplitude of the FEsignal because the amplitude level of the FE signal in the CD-R is lowerthan that in the CD due to a difference in absorptivities between theCD-R and the CD.

[0131] Furthermore, although the discrimination between a single-layerDVD and a double-layer DVD is performed using the maximum value of theENV signal in this first embodiment of the invention, it may beperformed using the maximum amplitude of the FE signal or the maximumvalue of the AS1L signal because there is a difference in the amplitudelevel of the FE signal or the AS1L signal level between the single-layerDVD and the double-layer DVD due to a difference in reflectivitiesbetween these DVDs.

[0132] [Embodiment 2]

[0133]FIG. 4 is a block diagram illustrating an optical disk apparatusin accordance with a second embodiment of the present invention. In FIG.4, the same reference numerals as those shown in FIG. 1 designate thesame or corresponding parts. The optical disk apparatus according tothis second embodiment of the invention can identify whether a disk setin the apparatus is a DVD or a CD. However, this apparatus cannotidentify whether the disk is a single-layer DVD or a double-layer DVD.

[0134] The optical disk apparatus according to this second embodiment isidentical to the optical disk apparatus according to the firstembodiment except that a band-pass filter 160 and a comparator 161 areincluded. The band-pass filter 160 transmits signals with frequencieswithin certain designated ranges. The comparator 161 outputs a highlevel signal when an input signal level exceeds a prescribed value.Therefore, whether signals within the pass band of the band pass filter160 are recorded in the disk 100 or not can be confirmed by the level ofthe output signal from the comparator 160. The pass band of the bandpass filter 160 is set at about 4 MHz.

[0135] A description is given of the operation of the optical diskapparatus according to this second embodiment.

[0136] When the disk 100 is put on the tray 149, the microcomputer 147drives the motor 118 so that the disk 100 is fixed to the rotation axis102 of the motor 101.

[0137] Next, the microcomputer 147 sets a prescribed value in a D/A(digital to analog) converter 145 to drive the transport motor 103through the power amplifier 139 so that the transport stage 104 movestoward the inner circumference of the disk 100, and drives the motor 128to select the focusing lens 110 and the actuator 112 for the DVD. Then,the microcomputer 147 rotates the motor 101. The rotating speed of themotor 101 is set at a rotating speed normalized for reproduction ofinformation on an inner circumference of a DVD. Further, themicrocomputer 147 sets a value in the D/A converter 141 to move thefocusing lens 110 once downward and then gradually upward toward thedisk 100. At this time, the switches 131 and 134 are open so that thefocusing coil and tracking coil of the actuator 112 are not driven inresponse to the FE signal and the TE signal. The operation describedabove is similar to the operation according to the first embodiment.

[0138] A description is now given of a method for discriminating a diskaccording to this second embodiment.

[0139] The maximum frequency of signals recorded in a DVD is about 4MHz, and the linear velocity of the DVD is about 3.3 m/s. In a CD, thelinear velocity is about 1.3 m/s, and the maximum frequency ofreproduced signals is about 700 KHz. So, when the CD is rotated with thelinear velocity of the DVD, the maximum frequency is given by 700KHz×(3.27/1.3)=1.8 MHz. Therefore, if the output from the comparator 161becomes high level when the focusing lens moves, it is found that asignal component of 4 MHz is included in the detected signal, and thedisk set in the apparatus is identified as a DVD. The operation afterthe discrimination of the disk is similar to the operation according tothe first embodiment.

[0140] In this second embodiment of the invention, the band-pass filter160 that transmits the signal component of 4 MHz is employed, and anoutput from the band-pass filter 160 is input to the comparator 161 todetect whether the output from the band-pass filter 160 includes thesignal component of 4 MHz or not, whereby the discrimination of the disk100 set in the apparatus is performed. However, the detection of thesignal component of 4 MHz may be performed by digitizing the inputsignal to the band-pass filter 160 and measuring the high-level orlow-level period of the signal. When the disk 100 is a DVD, thehigh-level or low-level period is about 125 ns. FIG. 5 shows a blockdiagram of an optical disk apparatus in this case.

[0141] The apparatus shown in FIG. 5 is different from the apparatusshown in FIG. 4 in that it includes a high-pass filter 700 (hereinafterreferred to as HPF) receiving the AS1 signal output from the adder 148,a comparator 701 receiving an output from the HPF 700, a counter 702receiving an output from the comparator 701, and a microcomputer 747receiving an output from the counter 702. The HPF 700 transmits only ahigh frequency component of an input signal. The cut-off frequency ofthe HPF 700 is determined so as to transmit a frequency component ofinformation recorded in the disk 100. Therefore, the frequency componentof the information recorded in the disk 100 is inputted to thecomparator 701. The comparator 701 is a digital circuit that converts aninput signal to a high-level signal or a low-level signal with a zerolevel as a reference. Therefore, an output from the comparator 701 is asignal obtained by digitizing the signal component of the informationrecorded in the disk 100. The counter 702 measures the period of thehigh-level or low-level of the input signal and sends the measured valueto the microcomputer 747. When the measured value inputted to themicrocomputer 747 is near 125 ns, the microcomputer 747 identifies thedisk set in the apparatus as a DVD because 125 ns corresponds to asignal component of 4 MHz. The operation of the microcomputer 747 otherthan the discrimination of the disk using the measured value is similarto the operation of the microcomputer 147.

[0142] As described above, in the optical disk apparatus shown in FIG.4, whether the AS1 signal corresponding to the amount of the reflectedlight from the disk 100 includes a signal component of a prescribedfrequency or not is detected by the band-pass filter 160 and thecomparator 161, whereby discrimination between a DVD having a high trackrecording density and a CD having a low track recording density ispossible. Furthermore, in the optical disk apparatus shown in FIG. 5,whether the AS1 signal corresponding to the amount of the reflectedlight from the disk 100 includes a signal component of a prescribedfrequency or not is detected by the high-pass filter 700, the comparator701, and the counter 702, whereby discrimination between a DVD having ahigh track recording density and a CD having a low track recordingdensity is possible.

[0143] [Embodiment 3]

[0144]FIG. 6 is a block diagram illustrating an optical disk apparatusin accordance with a third embodiment of the present invention. In FIG.6, the same reference numerals as those shown in FIG. 1 designate thesame or corresponding parts. The apparatus according to this thirdembodiment is identical to the apparatus according to the firstembodiment except that an actuator 172, a focusing lens 170, and ahologram 171 are employed in place of the actuators 112 and 127 and thefocusing lenses 110 and 126.

[0145] The optical system comprising the actuator 172, the focusing lens170, and the hologram 171 will be explained with reference to aschematic diagram shown in FIG. 7. The hologram 171 is located in thecenter of the optical axis of the light beam 150. The light beam 150traveling through the focusing lens 170 forms a focal point for the CD(F_(CD)) and a focal point for the DVD (F_(DVD)). The focal point F_(CD)is more distant from the focusing lens 170 than the focal point F_(DVD).The distance between the focal point F_(CD) and the focal point F_(DVD)is about 300 μm. In addition, the intensity of the focal point F_(DVD)is about twice as high as the intensity of the focal point F_(CD).

[0146] In FIG. 6, as in the first embodiment of the invention, when thedisk 100 is put on the tray 149, the microcomputer 147 drives the motor118 so that the disk 100 is fixed to the rotation axis 102 of the motor101. Next, the microcomputer 147 drives the transport motor 103 throughthe power amplifier 139 to move the transport stage 104 toward the innercircumference of the disk 100. Then, the microcomputer 147 rotates themotor 101. The rotating speed of the motor 101 is set at a rotatingspeed normalized for reproduction of information on an innercircumference of a DVD. When the motor 101 reaches the set rotatingspeed, the motor 101 sends an OK signal to the terminal a of themicrocomputer 147. Receiving the OK signal, the microcomputer 147 sets avalue in the D/A converter 141 to move the focusing lens 170 oncedownward and then gradually upward. At this time, the switches 131 and134 are open.

[0147] When the focusing lens 170 reaches the uppermost position, themicrocomputer 147 discriminates the disk 100. As the result of thediscrimination, when the disk 100 is identified as a CD-R, themicrocomputer 147 drives the motor 118 to move the tray 149 so that thedisk 100 is ejected from the apparatus. When the disk 100 is identifiedas a CD, the microcomputer 147 again moves the focusing lens 170downward and then gradually upward, and closes the switch 131 at thetiming when the ENV signal exceeds a prescribed level and the FE signalcrosses the zero level for the first time, thereby performing thefocusing control.

[0148] The reason why the moving direction of the focusing lens 170 ischanged between the CD and the DVD when the focusing control isperformed will be described hereinafter.

[0149] FIGS. 8(a)-8(c) show waveforms of the FE signal and the ENVsignal when the focusing lens 170 moves once downward and then graduallyupward. The abscissa shows time. In the optical system producing the twofocal points F_(CD) and F_(DVD) shown in FIG. 7, the FE signal and theENV signal change at the focal points F_(CD) and F_(DVD). In thesingle-layer DVD shown in FIG. 8(a) and the double-layer DVD shown inFIG. 8(b), since the focal point F_(CD) is more distant from thefocusing lens 170 than the focal point F_(DVD) as shown in FIG. 7, boththe FE signal and the ENV signal change at the focal point F_(CD) first(right side in the figure) and then at the focal point F_(DVD) (leftside in the figure). Therefore, when the disk 100 is a DVD, the focusinglens 170 is moved once upward and then gradually downward, and thefocusing control is performed at the time when the FE signal crosses thezero level for the first time (time t12 shown in FIG. 8(a) for thesingle-layer DVD) or the second time (time t13 shown in FIG. 8(b) forthe double-layer DVD). When the disk 100 is a CD, the focusing lens 170is moved once downward and then gradually upward, and the focusingcontrol is performed at the timing when the ENV signal exceeds aprescribed value and the FE signal crosses the zero level for the firsttime (time t11 in FIG. 8(c)). The reason why the ENV signal is taken asa condition for the CD shown in FIG. 8(c) is that the waveform shown bythe dotted line (time t10) appears in the FE signal at the surface ofthe base substrate.

[0150] A description is now given of a method of discriminating the disk100 using the microcomputer 147.

[0151] The microcomputer 147 receives the FE signal, the AS1L signal,and the ENV signal while the focusing lens 170 gradually moves upward,and measures the maximum values of these signals.

[0152] FIGS. 9(a)-9(d) show waveforms of the ENV signals and the AS1Lsignals in the single-layer DVD, the double-layer DVD, the CD, and theCD-R, respectively, when the focusing lens 170 gradually moves upward.

[0153] In FIGS. 9(a)-9(d), senv, Tenv, Uenv, and Venv show the maximumvalues of the ENV signals, and Sas, Tas, Uas, and Vas show the maximumvalues of the AS1L signals, within the period of time during which thefocusing lens 170 moves.

[0154] The ENV signal and the AS1L signal become high level when thefocal point F_(CD) and the focal point F_(DVD) are on the informationsurface of the disk, respectively. Among the maximum values of the ENVsignals, i.e., Senv, Tenv, Uenv, and Venv, in the single-layer DVD, thedouble-layer DVD, the CD, and the CD-R, respectively, Senv is thehighest value, Tenv is approximately equal to Uenv, and Venv is thesmallest value. Further, among the maximum values of the AS1L signals,i.e., Sas, Tas, Uas, and Vas, in the single-layer DVD, the double-layerDVD, the CD, and the CD-R, respectively, Sas and Uas are large andapproximately equal to each other, Tas is smaller than Uas, and Vas isthe smallest value. The reason why the maximum values Tenv and Tas inthe double-layer DVD are smaller than the maximum values Senv and Sas inthe single-layer DVD is that the reflectivity of the first layer of thedouble-layer DVD is lower than the reflectivity of the single-layer DVD.

[0155] The reason why the maximum level of the ENV signal due to thefocal point F_(CD) in the CD (Uenv) is lower than the maximum level ofthe ENV signal due to the focal point F_(DVD) in the single-layer DVD(Senv) is that the amount of light at the focal point F_(CD) is about50% of the amount of light at the focal point F_(DVD). In addition, thereason why the maximum level of the ENV signal due to the focal pointF_(DVD) in the CD (Uenv) is lower than the maximum level of the ENVsignal due to the focal point F_(DVD) in the single-layer DVD (Senv) isthat the focal point F_(DVD) is designed for a 0.6 mm thick basesubstrate and, therefore, the light beam is defocused.

[0156] The differences in the ENV signals and the AS1L signals betweenthe CD and the CD-R, i.e., the difference between Uenv and Venv and thedifference between Usa and Vas, are caused by the fact that theabsorptivity of the CD-R for light of 650 nm wavelength is larger thanthat of CD.

[0157] The microcomputer 147 stores Was, in advance, that satisfies therelationships, Vas<Was<Uas, Vas<Was<Tas, and Vas<Was<Sas, and comparesthe maximum value of the AS1L signal with Was. When the maximum value issmaller than Was, the microcomputer 147 identifies the disk 100 set inthe apparatus as a CD-R. In this case, the microcomputer 147 drives themotor 118 to move the tray 149 so that the disk 100 is ejected from theapparatus.

[0158] Then, the microcomputer 147 calculates Senv/Sas, Tenv/Tas, andUenv/Uas. Senv/Sas is approximately equal to Tenv/Tas. Uenv/Uas issmaller than Senv/Sas and Tenv/Tas.

[0159] The microcomputer 147 stores a prescribed value Z in advance andcompares a value obtained by dividing the maximum value of the ENVsignal by the maximum value of the AS1L signal with the value Z, wherebythe microcomputer 147 identifies whether the disk 100 set in theapparatus is a DVD or a CD.

[0160] A description is given of the value Z.

[0161] Initially, Senv/Sas, Tenv/Tas, and Uenv/Uas are measured for astandard disk, and the value Z is determined on the basis of the resultof the measurement. In an apparatus where the intensity of the focalpoint F_(DVD) is about twice as high as the intensity of the focal pointF_(CD), the value Z is about 6 in the single-layer DVD and thedouble-layer DVD and about 2 in the CD. Therefore, Z takes a valuebetween 2 and 6. In order to perform accurate discrimination of the diskeven when the characteristics of the disk vary, Z is set at a value thatsatisfies 6/Z=Z/2. So, Z is about 4. FIG. 23 shows the relationshipbetween the value Z and the disk. When the value obtained by dividingthe maximum value of the ENV signal by the maximum value of the AS1Lsignal is larger than 4, the disk is identified as a DVD. When the valueis smaller than 4, the disk is identified as a CD. However, since theresult of the division varies with a difference in amplification factorsbetween the ENV signal and the AS1L signal, when the amplificationfactors are changed, the value Z must be changed according to theamplification factors. Further, when the ratio of the intensity of thefocal point F_(DVD) to the intensity of the focal point F_(CD) ischanged, the value for the comparison must be changed according to theintensity ratio.

[0162] As described above, according to the third embodiment of thepresent invention, the maximum values of the AS1L signal and the ENVsignal are measured, the maximum value of the ENV signal is divided bythe maximum value of the AS1L signal, and the result of the division iscompared with a prescribed reference value. Therefore, in an opticaldisk apparatus utilizing an optical head having two focal points, i.e.,a focal point for reproducing a disk of a thick base substrate and afocal point for reproducing a disk of a thin base substrate, it ispossible to discriminate between a DVD having a thin base substrate anda CD having a thick base substrate.

[0163] Further, when the microcomputer 147 identifies the disk 100 setin the apparatus is a CD having a thick base substrate, themicrocomputer 147 sets a prescribed value in the D/A converter 141 tomove the focusing lens 170 toward the disk 100. Meanwhile, themicrocomputer 147 detects the timing for performing the focusing controland closes the switch 131 at this timing, thereby performing thefocusing control. Therefore, in the optical disk apparatus utilizing anoptical head having two focal points, i.e., a focal point forreproducing a disk of a thick base substrate and a focal point forreproducing a disk of a thin base substrate, the focusing control can benormally performed for the CD.

[0164] Furthermore, when the microcomputer 147 identifies the disk 100as a DVD having a thin base substrate, the microcomputer 147 sets aprescribed value in the D/A converter 141 to move the focusing lens 170downward, i.e., away from the disk 100. Meanwhile, the microcomputer 147detects the timing for performing the focusing control and closes theswitch 131 at this timing, thereby performing the focusing control.Therefore, in the optical disk apparatus utilizing an optical headhaving two focal points, i.e., a focal point for reproducing a disk of athick base substrate and a focal point for reproducing a disk of a thinbase substrate, the focusing control can be normally performedregardless of the thickness of the base substrate.

[0165] [Embodiment 4]

[0166]FIG. 10 is a block diagram illustrating an optical disk apparatusin accordance with a fourth embodiment of the present invention. In FIG.10, the same reference numerals as those shown in FIG. 6 designate thesame or corresponding parts. Reference numeral 411 designates aphotodetector, numeral 447 designates a microcomputer, numeral 450designates an I/V converter, numeral 451 designates a low-pass filter,numerals 452 and 461 designate A/D converters, numeral 453 designates avariable amplifier, numerals 454 and 462 designate adders, and numeral455 designates a D/A converter.

[0167] The photodetector 411 has a light responsive surface divided intofive parts. That is, a light responsive surface is added to thephotodetector 111 according to the third embodiment. FIG. 11 is aschematic diagram showing the photodetector 411. As shown in FIG. 11,the photodetector 411 according to this fourth embodiment has five lightresponsive parts A, B, C, D, and E whereas the photodetector 111according to the third embodiment has four light responsive parts A, B,C, and D. The light responsive parts A, B, C, and D constitute an innerregion of the photodetector 411, and the inner region is about 200 μmalong each side. The light responsive part E constitutes an outer regionof the photodetector 411, and the outer region is about 2 mm along eachside.

[0168] An output from the adder 148, i.e., a signal obtained by addingoutput signals from the light responsive parts A, B, C, and D, is calledan AS1L signal hereinafter. Therefore, as in the third embodiment of theinvention, an output from the differential amplifier 117 becomes an FEsignal that shows an error between the focal point of the light beam 150and the information face of the disk 100. In addition, an output fromthe differential amplifier 125 becomes a TE signal that shows an errorbetween the focal point of the light beam 150 and the track on the disk100. An output from the light responsive part E is sent to the I/Vconverter 450. An output from the I/V converter 450 is sent to the adder462 and the LPF 460. An output signal from the adder 462 is a signalobtained by adding output signals from all the light responsive parts ofthe photodetector 411, and this signal is called an ASL signalhereinafter. Likewise, an output signal from the LPF 451 is called anASL signal, an output signal from the I/V converter 450 is called an AS2signal, and an output signal from the LPF 460 is called an AS2L signal.The ASL signal is sent to the A/D converter 461. The microcomputer 447receives an output from the A/D converter 461 and receives the AS2Lsignal through the A/D converter 452. The I/V converter 450 operates inthe same way as the I/V converter 120. Likewise, the LPFs 451 and 460and the A/D converters 461 and 452 operate in the same way as the LPF165 and the A/D converter 142, respectively. The amplifier 453 canchange the amplification factor in response to a command from themicrocomputer 447. The adder 454 and the D/A converter 455 operate inthe same way as the adder 132 and the D/A converter 141, respectively.

[0169] The operation of the optical disk apparatus shown in FIG. 10 willbe described using a flow chart shown in FIG. 12.

[0170] When the disk 100 is put on the tray 149, the microcomputer 447drives the motor 118 to set the disk 100 to the rotation axis 102 of themotor 101 (step S1).

[0171] Next, the microcomputer 447 drives the transport motor 103through the D/A converter 145 and the power amplifier 139 to move thetransport stage 104 toward the inner circumference of the disk 100 (stepS2). Then, the microcomputer 447 rotates the motor 101 (step S3). Therotating speed of the motor 101 is set at a rotating speed normalizedfor reproduction of information on an inner circumference of a DVD.

[0172] Further, the microcomputer 447 discriminates the disk 100 toidentify whether the disk 100 is a DVD, a CD, or a CD-R (step S4). Amethod of discriminating the disk will be described later. The systemfor the discrimination is constructed so that the position of thefocusing lens 170 at the completion of the discriminating process isnearer to the disk 100 than the position of the focusing lens 170 whenthe focusing control is normally performed.

[0173] A description is given of the operation of the apparatus when thedisk 100 is identified as a DVD.

[0174] The microcomputer 447 sets an amplification factor of theamplifier 453 on the basis of a value AS1Lp (p means “peak”) that ismeasured in the discriminating process (step S5). Next, through the D/Aconverter 141, the adder 132, and the power amplifier 133, themicrocomputer 447 moves the focusing lens 170 gradually downward. The FEsignal detected during the downward movement of the lens 170 isamplified by the amplifier 453 and A/D converted by the A/D converter140, and the timing when the FE signal crosses the zero level for thefirst time (hereinafter referred to as zero cross timing) is detected onthe basis of an output from the A/D converter 140 (step S6). When thezero cross timing is detected, the output from the D/A converter 141 ismade zero and the switch 131 is closed, thereby performing the focusingcontrol (step S6). The AS1Lp signal will be described later.

[0175] A description is given of the operation of the apparatus when thedisk 100 is identified as a CD.

[0176] As in the case of the DVD, the microcomputer 447 sets anamplification factor of the amplifier 453 on the basis of the value AS1Lmeasured in the discriminating process (step 7). Further, themicrocomputer 447 sets the rotating speed of the motor 101 at a rotatingspeed normalized for reproduction of information on an innercircumference of a CD.

[0177] Next, the focusing lens 170 is moved once downward (step S8) andthen gradually upward, and the timing when the ENV signal output fromthe envelope detector 143 exceeds a prescribed level for the first timeand the FE signal crosses the zero level for the first time is detectedon the basis of the output from the A/D converter 140 (step S9). Whenthe zero cross timing is detected, the output from the D/A converter 141is made zero and the switch 131 is closed, thereby performing thefocusing control (step S9).

[0178] The reason why the moving direction of the focusing lens 170 ischanged between the CD and the DVD is as described for the thirdembodiment of the invention. Therefore, when a DVD is set in theapparatus, since the step of moving the focusing lens once downward isdispensed with, it is possible to start the signal reproduction within ashort time, compared to the case where a CD is set in the apparatus.Therefore, when DVDs are frequently set in the apparatus as comparedwith CDs, the signal reproduction can be started within a short time onthe average.

[0179] When the disk 100 is identified as a CD-R, the motor 118 isdriven to move the tray 149 so that the disk 100 is ejected from theapparatus (step S1).

[0180] Next, a method of discriminating a disk using the microcomputer447 will be described.

[0181] FIGS. 13(a)-13(c) show levels of an FE signal, an ENV signal, anAS1L signal, and an ASL signal, and an ENV/ASL value which is obtainedby dividing the ENV signal level by the AS1L signal level, for asingle-layer DVD, a double-layer DVD, and a CD, respectively.

[0182] The ENV signal and the AS1L signal change due to the focal pointF_(CD) for the CD and the focal point F_(DVD) for the DVD. In addition,the FE signal has a level change, generally called an S curve, when thefocal point F_(CD) (F_(DVD)) passes through the information face of thedisk.

[0183] According to an experiment, in case of the DVD, ENV/ASL attains amaximum value when the focal point F_(DVD) is on the information face.The reason is as follows. Since the ASL signal is a low frequencycomponent of the light beam reflected by the disk, ENV/ASL shows theratio of modulated amount of the light beam irradiating the disk by thepits on the disk. Therefore, when the focal point suitable for the diskset in the apparatus is on the information face of the disk, informationrecorded in the disk is reproduced with high efficiency. So, in case ofthe DVD, ENV/ASL attains a maximum value when the focal point F_(DVD) ison the information face of the disk. In case of the single-layer DVD,ENV/ASL attains a maximum value at time t31 in the waveform shown inFIG. 13(a). In case of the double-layer DVD, at times t32 and t33 in thewaveform shown in FIG. 13(b) where the focal point F_(DVD) is on thefirst and second information faces of the disk, respectively, ENV/ASLattains a maximum value. In case of the CD, ENV/ASL attains a maximumvalue at time t30 in the waveform shown in FIG. 13(c) where the focalpoint F_(CD) is on the information face of the disk.

[0184] Although in this fourth embodiment the ENV signal is obtainedfrom the amount of light ASL received by the light responsive parts A,B, C, D, and E of the photodetector 411, the ENV signal may be obtainedfrom the amount of light-AS1L received by the light responsive parts A,B, C, and D. Further, although ENV is divided with ASL, AS1L may be usedin place of ASL. In this case, under the condition where ENV/ASL attainsa maximum value, a value of AS1L/AS2L, which is obtained by dividing theAS1L level by the AS2L level that is obtained by subtracting the AS1Llevel from the ASL level, is larger in the single-layer DVD than in thedouble-layer DVD and the CD. That is, in the single-layer DVD, theintensity of light beam in the center of the photodetector 411 isincreased.

[0185] The reason will be described using FIGS. 24(a) and 24(b). FIGS.24(a) and 24(b) show conditions where ENV/ASL attains a maximum valuefor a single-layer DVD, a double-layer DVD, and a CD. More specifically,FIG. 24(a) shows the positional relationships between the informationface of the disk 100 and the focal points F_(DVD) and F_(CD), and FIG.24(b) shows reflected beams from the information face of the disk 100 tothe photodetector 411.

[0186] Initially, the single-layer DVD will be described. In thesingle-layer DVD, ENV/ASL attains a maximum value when the focal pointF_(DVD) is on the information face. The reflected beam from theinformation face of the disk 100 is narrowed by the detection lens 113and applied to the photodetecter 411 through the cylindrical lens 116.Therefore, the reflected beam RB_(DVD) of the beam for the DVD(hereinafter referred to as DVD beam) forms a focal point in the centerof the photodetector 411. However, since the focal point F_(CD) is noton the information face of the disk, the reflected beam RB_(CD) of thebeam for the CD (hereinafter referred to as CD beam) is incident on theentire surface of the photodetector 411 and irradiates the surfacedimly.

[0187] Next, the double-layer DVD will be described. In the double-layerDVD, ENV/ASL attains a maximum value when the focal point F_(DVD) is onthe first information face or the second information face. In thefigure, the focal point F_(DVD) is on the first information face.AS1L/AS2L obtained when the focal point F_(DVD) is on the firstinformation face is approximately equal to AS1L/AS2L obtained when thefocal point F_(DVD) is on the second information face.

[0188] In the double-layer DVD, the reflected beam RB_(DVD1) of the DVDbeam from the first information face forms a focal point in the centerof the photodetector 411. The DVD beam and the CD beam traveling throughthe first information face are reflected by the second information faceto be a reflected beam RB_(DVD2) and a reflected beam RB_(CD),respectively, and are incident on the entire surface of thephotodetector 411 because the focal point F_(CD) of the CD beam and thefocal point F_(DVD) of the DVD beam passing through the firstinformation face are not on the information face.

[0189] Since the reflectivity at the information face of thesingle-layer DVD is higher than the reflectivity at the informationfaces of the double-layer DVD, the amount of the inner side light beamincident on the photodetector 411 in the single-layer DVD (the reflectedbeam RB_(DVD)) is larger than the amount of the inner side light beamincident on the photodetector 411 in the double-layer DVD (the reflectedbeam RB_(DVD1)). In case of the double-layer DVD, the reflected beamRB_(DVD2) of the DVD beam from the second information face is incidenton the entire surface of the photodetector 411 and the reflected beamRB_(CD1,2) of the CD beam from the first and second information faces isadded to the reflected beam RB_(DVD2). So, the amount of the outer sidelight beam incident an the photodetector 411 in the double-layer DVD islarger than the amount of the outer side light beam incident on thephotodetector 411 in the single-layer DVD (the reflected beam RB_(CD)).Therefore, as described above, AS1L/AS2L is larger in the single-layerDVD than in the double-layer DVD.

[0190] Finally, the CD will be described. In the CD, ENV/ASL attains amaximum value when the focal point F_(CD) is on the information face ofthe disk. Therefore, the reflected beam RB_(CD) of the CD beam forms afocal point in the center of the photodetector 411. The reflected lightRB_(DVD) of the DVD beam is incident on the entire surface of thephotodetector 411 because the focal point F_(DVD) is not on theinformation face.

[0191] Since the intensity of the focal point F_(DVD) is higher than theintensity of the focal point F_(CD), the amount of the inner side lightbeam incident on the photodetector 411 in the single-layer DVD (thereflected beam RB_(DVD)) is larger than the amount of the inner sidelight beam incident on the photodetector 411 in the CD (the reflectedbeam RB_(CD)). In case of the CD, since the reflected beam RB_(DVD) ofthe DVD beam is incident on the entire surface of the photodetector 411,the amount of the outer side light beam incident on the photodetector411 is larger than the amount of the outer side light beam incident onthe photodetector 411 in the single-layer DVD (the reflected beamRB_(CD)) Therefore, as described above, AS1L/AS2L is larger in thesingle-layer DVD than in the CD.

[0192] According to the experiment, AS1L/AS2L in the single-layer DVD isabout 1.5 times as large as those in the double-layer DVD and the CD.Further, the level ENVp of the ENV signal under the condition thatENV/ASL attains a maximum value is higher in the single-layer DVD thanin the double-layer DVD and the CD. In case of a disk having a standardreflectivity, the maximum value ASL_(max) of ASL is approximately thesame in a single-layer DVD, a double-layer DVD, and a CD.

[0193] A description is now given of a method for discriminating asingle-layer DVD.

[0194] While moving the focusing lens 170 in the direction perpendicularto the information face of the disk 100, ENV/ASL is calculated, andAS1Lp, AS2Lp, ASLp, and ENVp at the moment when the ENV/ASL attains amaximum value are stored. Meanwhile, the maximum value ASL_(max) of ASLwithin the period of time during which the focusing lens 170 moves ismeasured. Using these values, a value Y is given by

Y=(ENVp/ASL _(max))×AS1Lp/AS2Lp

[0195] The value Y is significantly larger in the single-layer DVD thanin the double-layer DVD and the CD. According to the experiment, thevalue Y in the single-layer DVD is about four times as large as those inthe double-layer DVD and the CD. Therefore, a value F intermediate thevalue Y in the single-layer DVD and the value Y in the double-layer DVDor the CD is calculated in advance, and this value F is compared withthe value Y, whereby it is identified whether the disk 100 is asingle-layer DVD or not. Since ASL_(max) is used, the value Y is notadversely affected by variations in the reflectivity of the disk.

[0196] Although in this fourth embodiment the discrimination isperformed using the value Y, a value Y2 obtained in the followingformula may be employed for the discrimination in place of the value Y.

Y2=AS1Lp/AS2Lp

[0197] Further, when the variation in the reflectivity of the disk issmall, a value Y3 obtained in the following formula may be employed forthe discrimination.

Y3=ENVp×AS1Lp/AS2Lp

[0198] The optical disk apparatus according to this fourth embodimentcan reproduce a single-layer DVD, a double-layer DVD, and a CD. However,in an apparatus for reproducing two disks, a single-layer DVD and a CD,it is possible to discriminate between the single-layer DVD and the CDusing the value Y. That is, discrimination between a disk having a thinbase substrate and a disk having a thick base substrate is possible.

[0199] Hereinafter, a method of discriminating between a double-layerDVD and a CD will be described.

[0200] While moving the focusing lens 170 in the direction perpendicularto the information face of the disk 100, ENV/ASL is calculated, andAS1Lp at the moment when the ENV/ASL attains a maximum value ismeasured. Meanwhile, the maximum value ASL_(max) of ASL within theperiod of time during which the focusing lens 170 moves is measured.Using these values, a value Z is given by

Z=ASLp/ASL _(max)

[0201] The value Z is larger in the double-layer DVD than in the CD. Thereason is as follows. In the double-layer DVD, when the focal pointF_(DVD) is on the first information face, the light beam travelingthrough the first information face is reflected by the secondinformation face, and most of the reflected light is incident on thephotodetector 411 because the distance between the first informationface and the second information face is as short as about 40 μm. Thesame may be said when the focal point F_(DVD) is on the secondinformation face.

[0202] Further, in the CD, when the focal point F_(DVD) is on theinformation face, the light beam forming the focal point F_(DVD) isreflected at the information face, and most of the reflected light isincident on the photodetector 411. Under this condition, ASL attains amaximum value because the amount of light at the focal point F_(DVD) islarger than the amount of light at the focal point F_(CD). Further, whenthe focal point F_(CD) is on the information face, the light beamforming the focal point F_(DVD) is reflected at the information face andbecomes a stray light, a part of which is not incident on thephotodetector 411, because the distance between the focal point F_(CD)and the focal point F_(DVD) is as long as about 300 μm. Therefore, theASL level is reduced as compared with the case where the focal pointF_(DVD) is on the information face.

[0203] According to the experiment, the value Z is about 1 in thedouble-layer DVD and about 0.5 in the CD. Therefore, when a value Gintermediate the value Z in the double-layer DVD and the value Z in theCD is calculated in advance and this value G is compared with the valueZ, discrimination between a double-layer DVD and a CD is possible.However, in the single-layer DVD, since the amount of light at the focalpoint F_(DVD) is larger than the amount of light at the focal pointF_(CD), even when a part the reflected light of the light beam formingthe focal point F_(CD) is not incident on the photodetector 411, ASLp isnot adversely affected. Therefore, the value Z is approximately 1.Although, in this fourth embodiment, discrimination between adouble-layer DVD and a CD is performed using the value Z, discriminationbetween a single-layer DVD and a CD is also possible. That is,discrimination between a disk having a thick base substrate and a diskhaving a thin base substrate is possible using the value Z.

[0204] The operation of the microcomputer 447 in the above-mentioneddiscriminating process will be described using a flow chart shown inFIGS. 14 and 15.

[0205] The microcomputer 447 substitutes L_(max) for a variable FODA(step S11) and sets a value of the variable FODA in the D/A converter141 (step S12), whereby the focusing lens 170 moves upward. Here,L_(max) satisfies that both the focal point F_(CD) and the focal pointF_(DVD) are positioned above the information surface of the disk. Thispoint in the flow chart is denoted as point a. Thereafter, therespective variables, AS1Lp, AS2Lp, ASLp, ENVp, ASL_(max), and Q_(max)are cleared (step S13). This point in the flow chart is denoted as pointb. After point b, a value obtained by subtracting S from the variableFODA is substituted for the variable FODA (step S14). Then, the variableFODA is set in the D/A converter (step S15). Here, S is much smallerthan L_(max) and a positive value. Therefore, an output value from theD/A converter 141 becomes small and is transmitted through the adder 132and the power amplifier 133 to the focusing lens 170, whereby thefocusing lens 170 moves slightly downward. In this state, themicrocomputer 447 calculates ENV/ASL and substitutes this value for thevariable Q (step S18). Then, the microcomputer 447 substitutes AS2L,AS1L, and ENV for the variables AS2Lp, AS1Lp, and ENVp, respectively(step S19). Thereafter, the microcomputer 447 compares the variableASL_(max) with ASL (step S20). When the variable ASL_(max) is smallerthan ASL, the microcomputer 447 substitutes ASL for the variableASL_(max) (step S21).

[0206] Next, when the variable FODA is larger than L_(min) (NO in stepS22), the processing returns to point b. When the variable FODA issmaller than L_(min) (YES in step S22), the operation proceeds to thenext step. This point in the flow-chart is denoted as point C. Here,L_(min) satisfies that both the focal point F_(CD) and the focal pointF_(DVD) are positioned below the information face of the disk.

[0207] During the processing from point a to point c, the focal pointF_(CD) and the focal point F_(DVD) pass through the information face ofthe disk once. The processing after point c is shown in FIG. 15.

[0208] The processing from point c to point d is similar to theprocessing from point b to point c mentioned above except that a valueobtained by adding S to the variable FODA is substituted for thevariable FODA (step S11 a), step S12 is followed by step S16, and theprocessing is concluded when the variable FODA becomes larger thanL_(max) (YES in step S22 a). During the processing from point c to pointd, the focal point F_(CD) and the focal point F_(DVD) pass through theinformation face of the disk once. Therefore, during the processing frompoint a to point d, the focal point F_(CD) and the focal point F_(DVD)pass through the information face of the disk twice. Thereby, the momentwhen ENV/ASL attains a maximum value is detected accurately. Further,during the processing from point b to point d, the microcomputer 447outputs a sine wave through the D/A converter 455 toward the adder 454,and the sine wave is applied to the focusing lens 170 through the phasecompensator 135 and the power amplifier 136, whereby the focusing lens170 vibrates in the direction perpendicular to the track on the disk.Since the vibration of the focusing lens 170 prevents the focal pointfrom being always positioned between the tracks, the informationrecorded on the tracks is easily reproduced, and an accurate level ofthe ENV signal is-measured.

[0209] FIGS. 16(a) and 16(b) show variations in the position of thefocusing lens 170 during the discrimination of the disk according to theabove-mentioned operation. In the figures, the abscissa shows time, andthe ordinate shows the position of the lens 170. The upward direction ofthe ordinate means that the lens 170 approaches the disk 100. The pointsa, c, and d shown in FIGS. 14 and 15 correspond to points a, c, and dshown in FIG. 16. When the discrimination is concluded, the focusinglens 170 is positioned above. When the disk 100 is a DVD, while movingthe focusing lens 170 gradually downward, the first zero cross point ofthe FE signal is detected to perform the focusing control. When the disk100 is a CD, the focusing lens 170 is moved once downward and thengradually upward and, during the upward movement of the lens 170, thefirst zero cross point of the FE signal is detected to perform thefocusing control.

[0210] Therefore, when a DVD is set in the apparatus, reproduction ofsignals can be started within a short time, compared to the case where aCD is set in the apparatus.

[0211] Next, a description is given of setting an amplification factorof the amplifier 453 on the basis of AS1Lp. The setting of theamplification factor is performed to secure an accurate detection of thetiming for performing the focusing control. Initially, the timing forperforming the focusing control will be described with reference to FIG.17.

[0212]FIG. 17 shows an FE signal in a single-layer DVD. The abscissashows time. As the focusing lens 170 moves downward, the focal pointF_(DVD) approaches the information face of the disk. The FE signal isnegative at first. When the focal point F_(DVD) reaches the informationface, the FE signal becomes zero and, thereafter, it becomes positive.The timing for performing the focusing control is shown by point f atwhich the focal point F_(DVD) is on the information face. At point f, itis detected that the FE signal exceeds the comparison level Lc. In orderto reduce the delay in the detection, the comparison level Lc must benear the zero level Lz. However, since the FE signal includes noise andthe like, it is impossible to make the comparison level Lc zero.Therefore, the comparison level Lc is not the zero level Lz.

[0213] By the way, the amplitude of the FE signal decreases with areduction in the reflectivity at the information face of the disk or areduction in the intensity of the light beam 150. Even though thecomparison level Lc is fixed, when the amplitude of the FE signaldecreases, the delay in the detection increases. In the worst case, theamplitude of the FE signal does not reach the comparison level Lc. Inthe figure, the FE signal with reduced amplitude is shown by the dottedline. In this case, the timing for performing the focusing controlcannot be detected, so that the focusing control cannot be performed.

[0214] The variation in the reflectivity of the information face of thedisk or the intensity of the light beam 150 appears as a level change ofthe AS1Lp signal when the focal point is on the information face. Thatis, the level of the AS1Lp signal reduces with a reduction in thereflectivity-of the information face of the disk. So, when theamplification factor of the amplifier 453 is set according to the levelof the AS1Lp signal when the focal point for the disk set in theapparatus, i.e., F_(DVD) or F_(CD), is on the information face, an FEsignal with a constant amplitude can be obtained even though thereflectivity of the information face varies. As a result, the timing forperforming the focusing control can be detected accurately and reliablywithout a reduction in the amplitude of the FE signal as shown by thedotted line in FIG. 17.

[0215] Now, an amplitude of the FE signal and a value of AS1Lp in astandard condition are represented by H and J, respectively. Since AS1Lpis proportional to the amplitude of the FE signal, when the amplitude ofthe FE signal is reduced to H/2, AS1Lp is reduced to J/2. Since AS1Lp isJ/2, i.e., 50% of that in the standard condition, the microcomputer 447doubles the amplification factor of the amplifier 453. Thereby, theamplitude of the FE signal inputted to the A/D converter 140 becomes H,i.e., the amplitude in the standard condition. As a result, the timingfor performing the focusing control can be detected with highreliability.

[0216] According to this fourth embodiment of the invention, in case ofthe DVD, ENV/ASL attains a maximum value when the focal point F_(DVD) ison the first information face (single-layer DVD) or when the focal pointF_(DVD) is on the first information face or the second information face(double-layer DVD). In case of the CD, ENV/ASL attains a maximum valuethen the focal point F_(CD) is on the information face. According to theexperiment, ENV/AS1L and ENV/ASL show similar characteristics, so thatENV/AS1L may be used in place of ENV/ASL. Further, although the ENVsignal is detected from the AS signal, it may be detected from the AS1signal.

[0217] While in this fourth embodiment of the invention a singlephotodetector 411 having a light responsive surface divided into fiveparts is employed, two photodetectors may be employed when the structureof the optical system is changed. FIG. 18 is a block diagramillustrating an optical disk apparatus including two photodetectors. Inthe figure, the same reference numerals as those shown in FIG. 10designate the same or corresponding parts. Reference numeral 111designates a photodetector, numeral 601 designates a half mirror, andnumeral 602 designates a photodetector. The photodetectors 111 and 602and the half mirror 601 are fixed onto the transport stage 104.

[0218]FIG. 19(a) and 19(b) are schematic diagrams illustrating thephotodetector 111 and the photodetector 602, respectively. As shown inthese figures, the photodetector 111 has four light responsive parts A,B, C, and D corresponding to the light responsive parts A, B, C, and Dof the photodetector 411 shown in FIG. 11, and the photodetector 602 hasa light responsive part (hatched part) corresponding to the lightresponsive part E of the photodetector 411. These photodetectors 111 and602 are fixed so that the center points P and Q are aligned with theoptical axis of incident light.

[0219] The light beam traveling through the cylindrical lens 116 isdivided into two beams by the half mirror 601, and one of the beams isincident on the photodetector 111 while the other is incident on thephotodetector 602. The photodetector 602 is positioned so that thedistance from the half mirror 601 to the photodetector 602 is equal tothe distance from the half mirror 601 to the photodetector 111.Therefore, input signals to the I/V converters 114, 115, 119, 120, and450 are similar to those in the apparatus shown in FIG. 10. Therefore,the operation of the apparatus shown in FIG. 18 is similar to theoperation of the apparatus shown in FIG. 10.

[0220] As described above, according to the fourth embodiment of thepresent invention, in an optical disk apparatus using an optical headhaving two focal points, i.e., a focal point for reproducing a diskhaving a thick base substrate and a focal point for reproducing a diskhaving a thin base substrate, the photodetector 411 detects theintensity of the reflected light in the center region and the intensityof the reflected light in the peripheral region. Therefore, it ispossible to discriminate between a DVD having a thin base substrate anda CD having a thick base substrate on the basis of the intensity ratio.

[0221] Further, since the amount of light incident on the photodetector411 when the ENV signal attains a maximum value is used for thediscrimination of the disk 100, the discrimination is accuratelyperformed.

[0222] Likewise, since the amount of light incident on the photodetector411 when a value obtained by dividing the ENV signal by the ASL signalattains a maximum value is used for the discrimination of the disk 100,the discrimination is accurately performed even when the reflectivity ofthe disk 100 varies.

[0223] Furthermore, the amount of light AS1Lp incident on the firstlight responsive region of the photodetector 411, the amount of lightAS2Lp incident on the second light responsive region of thephotodetector 411, and the amplitude ENVp of the information signal aremeasured, and the ratio of AS1Lp×ENVp to AS2Lp is used for thediscrimination of the disk 100, whereby the accuracy of thediscrimination is improved.

[0224] Furthermore, the amount of light AS1Lp incident on the firstlight responsive region of the photodetector 411, the amount of lightAS2Lp incident on the second light responsive region of thephotodetector 411, the amplitude ENVp of the information signal, andASL_(max) are measured, and the ratio of AS1Lp×ENVp to AS2Lp×ASL_(max)is used for the discrimination of the disk 100, the discrimination isaccurately performed even when the reflectivity of the disk 100 varies.

[0225] The same effects as mentioned above are attained in the opticaldisk apparatus shown in FIG. 18 including the two photodetectors 111 and602.

[0226] Furthermore, according to the fourth embodiment of the presentinvention, in an optical disk apparatus using an optical head having twofocal points, i.e., a focal point for reproducing a disk having a thickbase substrate and a focal point for reproducing a disk having a thinbase substrate, the photodetector 411 detects the intensity of thereflected light in the center region and the intensity of the reflectedlight in the peripheral region. Therefore, it is possible todiscriminate between a disk having a single information face and a diskhaving two information faces on the basis of the intensity ratio.

[0227] Further, since the amount of light incident on the photodetector411 when the ENV signal attains a maximum value is used for thediscrimination of the disk 100, the discrimination is accuratelyperformed.

[0228] Likewise, since the amount of light incident on the photodetector411 when a value obtained by dividing the ENV signal by the ASL signalattains a maximum value is used for the discrimination of the disk 100,the discrimination is accurately performed even when the reflectivity ofthe disk 100 varies.

[0229] Furthermore, the amount of light AS1Lp incident on the firstlight responsive region of the photodetector 411, the amount of lightAS2Lp incident on the second light responsive region of thephotodetector 411, and the amplitude ENVp of the information signal aremeasured, and the ratio of AS1Lp×ENVp to AS2Lp is used for thediscrimination of the disk 100, whereby the accuracy of thediscrimination is improved.

[0230] Furthermore, the amount of light AS1Lp incident on the firstlight responsive region of the photodetector 411, the amount of lightAS2Lp incident on the second light responsive region of thephotodetector 411, the amplitude ENVp of the information signal, andASL_(max) are measured, and the ratio of AS1Lp×ENVp to AS2Lp×ASL_(max)is used for the discrimination of the disk 100, the discrimination isaccurately performed even when the reflectivity of the disk 100 varies.

[0231] The same effects as mentioned above are attained in the opticaldisk apparatus shown in FIG. 18 including the two photodetectors 111 and602.

[0232] Furthermore, according to the fourth embodiment of the presentinvention, in an optical disk apparatus using an optical head having twofocal points, i.e., a focal point for reproducing a disk having a thickbase substrate and a focal point for reproducing a disk having a thinbase substrate, when it is detected from the output of the photodetector411 that a focal point appropriate for the disk 100 set in the apparatusis present in the vicinity of the information face, the amplificationfactor of the variable amplifier 453 that amplifies the focal pointerror signal is changed according to the amount of light AS1Lp.Therefore, even when the reflectivity of the disk 100 varies, theamplitude of the FE signal is constant, whereby an accurate timing forperforming the focusing control is obtained.

[0233] Further, after changing the amplification factor of the amplifier453, focusing control is performed at the timing when the output signalfrom the amplifier 453 reaches a prescribed level. Therefore, it isavoided that the focusing control is performed at a wrong timing due tonoise or the like.

[0234] Furthermore, since the amount of light incident on thephotodetector 411 when a value obtained by dividing the ENV signal bythe ASL signal attains a maximum value is used for the timing detection,even when the reflectivity of the disk 100 varies, the presence of theappropriate focal point in the vicinity of the information face can bedetected at accurate timing.

[0235] Furthermore, since each of the two focal points, i.e., the focalpoint for reproducing a disk having a thick base substrate and the focalpoint for reproducing a disk having a thin base substrate, passesthrough the information face twice, the amount of reflected light fromthe disk 100 is accurately detected.

[0236] [Embodiment 5]

[0237]FIG. 20 is a block diagram illustrating an optical disk apparatusin accordance with a fifth embodiment of the present invention. In thefigure, the same reference numerals as those shown in FIG. 6 designatethe same or corresponding parts. Reference numeral 500 designates asignal processing circuit, and numeral 547 designates a microcomputer.

[0238] The signal processing circuit 500 reproduces information recordedin the disk 100 according to an output signal AS1 from the adder 148,converts the information to digital data, and sends the digital data tothe microcomputer 547. The signal processing circuit 500 can reproduceboth the CD and the DVD. The switching of the operation is commanded bythe microcomputer 547.

[0239] The operation of the apparatus shown in FIG. 20 will be describedusing waveforms shown in FIGS. 21(a) and 21(b). The waveform in FIG.21(a) shows the position of the focusing lens 170, and the waveform inFIG. 21(b) shows the FE signal as an output signal from the differentialamplifier 117.

[0240] In FIG. 20, when the disk 100 is put on the tray 149, themicrocomputer 547 drives the motor 118 so that the disk 100 is fixed tothe rotation axis 102 of the motor 101. Next, the microcomputer 547rotates the motor 101. The rotating speed of the motor 101 is set at arotating speed of an inner circumference of a CD. The microcomputer 547sets a value in the D/A converter 141 to move the focusing lens 170 oncedownward (t210 in FIG. 21(a)). Thereafter, the microcomputer 547 movesthe focusing lens 170 gradually upward. At this time, the switches 131and 134 are open. Since an output signal from the D/A converter 141 issent through the adder 132 and the power amplifier 133 to the actuator172, the level of the output signal from the D/A converter 141corresponds to the position of the focusing lens 170.

[0241] While moving the focusing lens 170 gradually upward, the switch131 is closed at the timing when the ENV signal exceeds a prescribedvalue and the FE signal crosses the zero level for the first time,thereby performing the focusing control. This timing is denoted by t211in FIG. 21(b). As already described for the third embodiment of theinvention, when the disk 100 is a CD, this timing for performing thefocusing control is the timing when the focal point F_(CD) is on theinformation face of the disk. Therefore, the focusing control isperformed so that the focal point F_(CD) is on the information face ofthe CD. Then, the microcomputer 547 closes the switch 134 to perform thetracking control. Further, the microcomputer 547 controls the signalprocessing circuit 500 to select the CD information reproducing circuit602. Therefore, the signal processing circuit 500 reproduces informationrecorded in the CD and sends data to the microcomputer 547. In FIGS.21(a) and 21(b), waveforms shown by dotted lines appear when thefocusing control is not performed, as described for the third embodimentof the invention.

[0242] Furthermore, the signal processing circuit 500 will be describedin detail with reference to FIGS. 21(c) and 21(d).

[0243]FIG. 21(c) is a block diagram showing the signal processingcircuit 500. In FIG. 21(c), a first input terminal 601 is connected tothe adder 148 and receives the AS1 signal. An output terminal 605 isconnected to the microcomputer 547. A CD information reproducing circuit602 is a circuit for reproducing information recorded in a CD. A DVDinformation reproducing circuit 603 is a circuit for reproducinginformation recorded in a DVD. A switch 606 selects a signal at terminala or a signal at terminal b according to a level of control terminal dand sends the signal to terminal c. A second input terminal 604 isconnected to the control terminal d of the switch 606.

[0244]FIG. 21(d) is a block diagram illustrating the CD informationreproducing circuit 602. An input terminal 704 receives the AS1 signal.An output terminal 705 is connected to the switch 606. A high-passfilter 700 eliminates a low frequency component. A comparator 701outputs a high level signal when the level of an input signal is higherthan zero, and outputs a low level signal when the level of the inputsignal is lower than zero. A periodic pattern detector 706 detects aperiodic pattern at the top of a frame in a signal formats of the CD. Aconverter 702 converts 17-bit input data to 8-bit data. A referencetiming for dividing input data to 17-bit data is based on an outputsignal from the periodic pattern detector 706. This conversion isperformed according to a conversion table based on EFM(eight-to-fourteen modulation) that is a CD system modulation process.In the EFM, 14-bit data within 17-bit data have information, and the14-bit data can take only 256 kinds of values. Therefore, the conversiontable converts 256 kinds of input data to 8-bit data corresponding tothe input data. An output signal from the converter 702 is sent to anerror corrector 703 wherein errors in the CD system are corrected.

[0245] Since the focal point F_(CD) is now on the information face ofthe CD, data corresponding to one of the 256 kinds of data on theconversion table is inputted to the converter 702. Therefore, the inputdata are correctly converted, whereby information recorded in the disk100 is reproduced.

[0246] A description is given of the operation when the disk 100 is aDVD. Although the disk 100 is a DVD, the timing for performing thefocusing control is the timing when the focal point F_(CD) is on theinformation face of the disk. Therefore, the focusing control isperformed so that the focal point F_(CD) is on the information face ofthe disk. The microcomputer 547 closes the switch 134 to perform thetracking control. Further, the microcomputer 547 controls the signalprocessing circuit 500 to select the CD information reproducing circuit602.

[0247] However, since the CD system modulation process is different froma modulation process for the DVD, the data inputted to the converter 702in the signal processing circuit 500 is different from the 256 kinds ofdata on the conversion table. So, the converter 702 does not output dataand, therefore, the error corrector 703 is not operated. In this case,no information is sent to the microcomputer 547.

[0248] When the microcomputer 547 knows that no information is sent fromthe signal processing circuit 500, it identifies the disk 100 as a DVD.Then, the microcomputer 547 opens the switches 131 and 134 to immobilizethe focusing control system and the tracking control system. Thesubsequent processing will be described using waveforms shown in FIGS.22(a) and 22(b). The waveform in FIG. 22(a) shows the position of thefocusing lens 170, and the waveform in FIG. 22(b) shows the FE signal asan output signal from the differential amplifier 117.

[0249] The microcomputer 547 sets the rotating speed of the motor 101 ata rotating speed of an inner circumference of a DVD. The microcomputer547 sets a value in the D/A converter 141 to move the focusing lens 170once toward the disk 100 (t310 in FIG. 22(a)). Thereafter, themicrocomputer 547 moves the focusing lens 170 gradually downward andcloses the switch 131 at the timing when the FE signal crosses the zerolevel for the first time, thereby performing the focusing control. Thistiming is denoted by t311 in FIG. 22(b). As already described for thethird embodiment of the invention, when the disk 100 is a DVD, thistiming for performing the focusing control is the timing when the focalpoint F_(DVD) is on the information face of the disk. Thereafter, themicrocomputer 547 closes the switch 134 to perform the tracking control.Further, the microcomputer 547 controls the signal processing circuit500 to select the DVD information reproducing circuit 603. Therefore,the signal processing circuit 500 reproduces information recorded in thedisk 100 and sends data to the microcomputer 547. In FIGS. 22(a) and22(b), waveforms shown by dotted lines appear when the focusing controlis not performed, as described for the third embodiment of theinvention.

[0250] In this fifth embodiment of the invention, the microcomputer 547starts the operation on the assumption that the disk 100 is a CD, it maystart the operation on the assumption that the disk 100 is a DVD. Inthis case, the rotating speed of the motor 101 is set at a rotatingspeed of an inner circumference of a DVD. The focusing lens 170 is movedonce upward and then gradually downward, and the focusing control isperformed at the first zero cross timing of the FE signal, and thetracking control is performed. The DVD information reproducing circuit603 is selected in the signal processing circuit 500. When noinformation is reproduced, the disk 100 is identified as a CD, and thefocusing control system and the tracking control system are immobilized.Then, the rotating speed of the motor 101 is set at a rotating speed ofan inner circumference of a CD. The focusing lens 170 is moved oncedownward and then gradually upward, and the focusing control isperformed at the timing when the ENV signal exceeds a prescribed leveland the FE signal crosses the zero level for the first time, and thetracking control is performed. In the signal processing circuit 500, theCD information reproducing circuit 602 is selected.

[0251] As described above, according to the fifth embodiment of theinvention, in an optical disk apparatus using an optical head having twofocal points, i.e., a focal point for reproducing a disk having a thickbase substrate and a focal point for reproducing a disk having a thinbase substrate, even when the focusing control is performed using aninappropriate focal point, the signal processing circuit 500 detectsthat the focusing control is performed with the inappropriate focalpoint. Therefore, it is possible to try the focusing control again withan appropriate focal point.

What is claimed:
 1. An optical disk apparatus for reproducinginformation recorded on an information face of a disk using an opticalhead having a first focal point for reproducing a disk having a thickbase substrate and a second focal point for reproducing a disk having athin base substrate, said apparatus comprising: a focal point movingdevice operable to move the first and second focal points in a directionperpendicular to the information face of the disk; a reflected lightdetecting device operable to detect a reflected light from the disk; afocus error detecting device operable to detect a focused state of alight beam irradiating the information face of the disk on the basis ofan output signal from said reflected light detecting device; a focuscontrol device operable to control focusing so that the focused state ofthe light beam becomes a desired state, on the basis of an output signalfrom said focus error detecting device; and a generating device operableto generate a timing signal for driving said focus control device on thebasis of an output signal from said focus error detecting device;wherein said focal point moving device is driven so that the focalpoints go away from the disk, and said focus control device is operatedin response to the timing signal; and when no information is reproduced,said focus control device is immobilized, and said focal point movingdevice is driven so that the focal points approach the disk, and saidfocus control device is operated in response to the timing signal.
 2. Anoptical disk apparatus for reproducing information recorded on aninformation face of a disk using an optical head having a first focalpoint for reproducing a disk having a thick base substrate and a secondfocal point for reproducing a disk having a thin base substrate, saidapparatus comprising: a focal point moving device operable to move thefirst and second focal points in a direction perpendicular to theinformation face of the disk; a reflected light detecting deviceoperable to detect a reflected light from the disk; a focus errordetecting device operable to detect a focused state of a light beamirradiating the information face of the disk on the basis of an outputsignal from said reflected light detecting device; a focus controldevice operable to control focusing so that the focused state of thelight beam becomes a desired state on the basis of an output signal fromsaid focus error detecting device; and a generating device operable togenerate a timing signal for driving said focus control device on thebasis of an output signal form said focus error detecting device;wherein said focal point moving device is driven so that the focalpoints approach the disk, and said focus control device is operated inresponse to the timing signal; and when no information is reproduced,said focus control device is immobilized, and said focal point movingdevice is driven so that the focal points go away from the disk, andsaid focus control device is operated in response to the timing signal.3. An optical disk apparatus for reproducing information recorded on aninformation face of a disk using an optical head having a first focalpoint for reproducing a disk having a thick base substrate and a secondfocal point for reproducing a disk having a thin base substrate, saidapparatus comprising: a focal point moving device operable to move thefirst and second focal points in a direction perpendicular to theinformation face of the disk; a reflected light detecting deviceoperable to detect a reflected light from the disk; a focus errordetecting device operable to detect a focused state of a light beamirradiating the information face of the disk on the basis of an outputsignal from said reflected light detecting device; a focus controldevice operable to control focusing so that the focused state of thelight beam becomes a desired state on the basis of an output signal fromsaid focus error detecting device; a generating device operable togenerate a timing signal for driving said focus control device on thebasis of an output signal from said focus error detecting device; and adiscriminating device operable to discriminate whether the disk set insaid apparatus is a disk having a thick base substrate or a disk havinga thin base substrate; wherein, when the disk set in said apparatus isdiscriminated as a disk having a thick base substrate, said focal pointmoving device is driven so that said focal points approach the disk, andsaid focus control device is operated in response to the timing signal.4. An optical disk apparatus for reproducing information recorded on aninformation face of a disk using an optical head having a first focalpoint for reproducing a disk having a thick base substrate and secondfocal point for reproducing a disk having a thin base substrate, saidapparatus comprising: a focal point moving device operable to move thefirst and second focal points in a direction perpendicular to theinformation face of the disk; a reflected light detecting deviceoperable to detect a reflected light from the disk; a focus errordetecting device operable to detect a focused state of a light beamirradiating the information face of the disk, on the basis of an outputsignal from said reflected light detecting device; a focus controldevice operable to control focusing so that the focused state of thelight beam becomes a desired state on the basis of an output signal fromsaid focus error detecting device; a generating device operable togenerate a timing signal for driving said focus control device on thebasis of an output signal from said focus error detecting device; and Adiscriminating device operable to discriminate whether the disk set insaid apparatus is a disk having a thick base substrate or a disk havinga thin base substrate; wherein, when the disk set in said apparatus isdiscriminated as a disk having a thin base substrate, said focal pointmoving device is driven so that the focal points go away from the disk,and said focus control device is operated in response to the timingsignal.
 5. An optical disk apparatus for reproducing informationrecorded on an information face of a disk using an optical head having afirst focal point for reproducing a disk having a thick base substrateand a second focal point for reproducing a disk having a thin basesubstrate, said apparatus comprising: a focal point moving deviceoperable to move the first and second focal points in a directionperpendicular to the information face of the disk; a reflected lightdetecting device operable to detect a reflected light from the disk; afocus error detecting device operable to detect a focused state of alight beam irradiating the information face of the disk on the basis ofan output signal from said reflected light detecting device; a focuscontrol device operable to control focusing so that the focused state ofthe light beam becomes a desired state on the basis of an output signalfrom said focus error detecting device; a generating device operable togenerate a timing signal for driving said focus control device on thebasis of an output signal from said focus error detecting device; and adiscriminating device operable to discriminate whether the disk set insaid apparatus is a disk having a thick base substrate or a disk havinga thin base substrate; wherein, when the disk set in said apparatus isdiscriminated as a disk having a thick base substrate, said focal pointmoving device is driven so that the focal points approach the disk, andsaid focus control device is operated in response to the timing signal;and when the disk set in said apparatus is discriminated as a diskhaving a thin base substrate, said focal point moving device is drivenso that the focal points go away from the disk, and said focusingcontrol device is operated in response to the timing signal.
 6. Anoptical disk apparatus for reproducing information recorded on aninformation face of a disk using an optical head having a first focalpoint for reproducing a disk having a thick base substrate and a secondfocal point for reproducing a disk having a thin base substrate, saidapparatus comprising: a focal point moving device operable to move thefirst and second focal points in a direction perpendicular to theinformation face of the disk; a reflected light detecting deviceoperable to detect a reflected light from the disk; a discriminatingdevice operable to discriminate whether the disk set in said apparatusis a disk having a thick base substrate or a disk having a thin basesubstrate; and an information face detecting device operable to detectthat a focal point of a light beam suitable for the disk is near theinformation face of the disk, from an output signal from said reflectedlight detecting device, while driving said focal point moving device sothat the first and second focal points pass through the information faceof the disk; wherein said discriminating device discriminates whetherthe disk set in said apparatus is a disk having a thick base substrateor a disk having a thin base substrate, on the basis of the ratio of amaximum value ASL_(max) of a signal output from said reflected lightdetecting device to a level ASLp of a signal output from said reflectedlight detecting device when the information face is detected by saidinformation face detecting device, while driving said focal point movingdevice so that the first and second focal points pass through theinformation face.
 7. The apparatus of claim 6, wherein said informationface detecting device is operable to detect that a focal point of alight beam suitable for the disk is near the information face of thedisk, on the basis of the ratio of a low frequency signal level of anoutput signal from the said reflected light detecting device to aninformation reproducing signal level of the output signal.
 8. An opticaldisk apparatus for reproducing information recorded on an informationface of a disk using an optical head having a first focal point forreproducing a disk having a thick base substrate and a second focalpoint for reproducing a disk having a thin base substrate, saidapparatus comprising: a focal point moving device operable to move thefirst and second focal points in a direction perpendicular to theinformation face of the disk; a reflected light detecting deviceoperable to detect a reflected light from the disk; and a discriminatingdevice operable to discriminate whether the disk set in said apparatusis a disk having a thick base substrate or a disk having a thin basesubstrate; wherein a maximum value AS1L_(max) of an output from saidreflected light detecting device and a maximum value ENV_(max) of anamplitude of an information reproducing signal are measured whiledriving said focal point moving device so that the first and secondfocal points pass through the information face of the disk, and saiddiscriminating device discriminates whether the disk set in saidapparatus is a disk having a thick base substrate or a disk having athin base substrate on the basis of the ratio of ENV_(max) toAS1L_(max).